diff --git a/docs/formats/FORMAT-app_process.md b/docs/formats/FORMAT-app_process.md
index 3efd46d..d2f15ce 100644
--- a/docs/formats/FORMAT-app_process.md
+++ b/docs/formats/FORMAT-app_process.md
@@ -641,13 +641,15 @@ Behavior:
 
 * If local `## Domains` is absent, `Steps.domain` still groups Business Flow steps, but Model Weave does not warn about unknown domain values unless `## Domain Sources` is present.
 * If local `## Domains` is present, `Steps.domain` is resolved by local Domain `id`.
-* Resolved local Domains are rendered as nested Business Flow groups using `Domains.parent`.
+* If `## Domain Sources` is also present, external Domains are loaded first and local `## Domains` override external definitions for the same `id`.
+* Resolved Domains are rendered as nested Business Flow groups using `Domains.parent`.
 * Domain `name` is used as the visible group label. If `name` is empty, `id` is used.
 * Domains that have no direct steps are still rendered when they are ancestors of a Domain that has steps.
 * Duplicate local Domain ids produce diagnostics.
-* Local Domain `parent` values must reference another local Domain id.
+* Local Domain `parent` values must reference another resolved Domain id. With `## Domain Sources`, this may be an imported external Domain id.
 * If a local Domain has an unknown parent, it is rendered as a root-level group and the parent diagnostic remains visible.
-* When a Color Scheme is active, resolved local Domain groups use `target=domain` and `kind=<Domains.kind>` for group colors.
+* If a local Domain overrides an external Domain `name`, `kind`, or `parent`, Model Weave reports a warning and uses the local value.
+* When a Color Scheme is active, resolved Domain groups use `target=domain` and `kind=<Domains.kind>` for group colors.
 * If `Steps.domain` is present but not found, Model Weave does not fall back to `Steps.lane`.
 * `Steps.lane` remains legacy-compatible layout-only placement and is only used when `Steps.domain` is empty.
 
@@ -670,10 +672,10 @@ Behavior:
 * If `## Domain Sources` is present, sources are loaded in table order and merged using the same Domain Source behavior as `domain_diagram` where practical.
 * If a source cannot be resolved, or resolves to a non-`domains` file, Model Weave reports a warning.
 * If `Steps.domain` does not match any merged Domain id, Model Weave reports a warning.
-* Domain Sources currently validate placement metadata, but Business Flow hierarchy rendering and Domain group coloring are driven by local `## Domains`.
+* If local `## Domains` is also present, local rows are applied after external sources and win for the same Domain `id`.
+* The merged Domain set drives Business Flow hierarchy rendering and Domain group coloring.
 * If `Steps.domain` is present but unresolved, Model Weave does not fall back to `Steps.lane`.
 * `Steps.lane` remains legacy-compatible layout-only placement and is only used when `Steps.domain` is empty.
-* Domain group coloring is applied only for resolved local `## Domains`. External Domain Source group coloring is planned for a later step.
 * Business Flow step node colors continue to use `target=app_process` and `Steps.kind`.
 
 #### Steps as the default flow
diff --git a/docs/ja/formats/FORMAT-app_process.md b/docs/ja/formats/FORMAT-app_process.md
index 670f5b7..c7c88af 100644
--- a/docs/ja/formats/FORMAT-app_process.md
+++ b/docs/ja/formats/FORMAT-app_process.md
@@ -641,13 +641,15 @@ Business Flow preview には table-based steps を使います。
 
 * ローカル `## Domains` がない場合でも、`Steps.domain` は Business Flow のStep groupingに使われます。ただし `## Domain Sources` がない限り、不明なdomain値の警告は出しません。
 * ローカル `## Domains` がある場合、`Steps.domain` はローカルDomain `id` で解決されます。
-* 解決されたローカルDomainは、`Domains.parent` を使って入れ子のBusiness Flow groupとして描画されます。
+* `## Domain Sources` もある場合、外部Domainsを先に読み込み、同じ `id` の定義はローカル `## Domains` が上書きします。
+* 解決されたDomainは、`Domains.parent` を使って入れ子のBusiness Flow groupとして描画されます。
 * 表示されるgroup labelにはDomain `name` が使われます。`name` が空の場合は `id` が使われます。
 * 直接Stepを持たないDomainでも、Stepを持つ子Domainの祖先であれば描画されます。
 * 重複したローカルDomain idは診断になります。
-* ローカルDomainの `parent` は、別のローカルDomain idを参照する必要があります。
+* ローカルDomainの `parent` は、解決済みDomain idを参照する必要があります。`## Domain Sources` がある場合は、importされた外部Domain idも参照できます。
 * ローカルDomainの `parent` が不明な場合、そのDomainはroot-level groupとして描画され、parent診断は表示され続けます。
-* Color Scheme が有効な場合、解決されたローカルDomain group は `target=domain` と `kind=<Domains.kind>` を使って色付けされます。
+* ローカルDomainが外部Domainの `name`, `kind`, `parent` を上書きする場合、警告を出し、ローカル値を使います。
+* Color Scheme が有効な場合、解決されたDomain group は `target=domain` と `kind=<Domains.kind>` を使って色付けされます。
 * `Steps.domain` が存在して解決できない場合でも、`Steps.lane` へはfallbackしません。
 * `Steps.lane` は legacy-compatible な layout-only 配置であり、`Steps.domain` が空の場合だけ使われます。
 
@@ -670,10 +672,10 @@ Business Flow preview には table-based steps を使います。
 * `## Domain Sources` がある場合、sourceはテーブル順に読み込まれ、可能な範囲で `domain_diagram` と同じDomain Source動作でマージされます。
 * sourceが解決できない場合、または `domains` 以外のファイルを指す場合、警告が出ます。
 * `Steps.domain` がマージ済みDomain idに一致しない場合、警告が出ます。
-* Domain Sources は配置metadataの検証に使われますが、Business Flow hierarchy rendering と Domain group coloring はローカル `## Domains` によって行われます。
+* ローカル `## Domains` もある場合、ローカル行は外部sourceの後に適用され、同じDomain `id` ではローカル定義が優先されます。
+* マージ済みDomain setが Business Flow hierarchy rendering と Domain group coloring に使われます。
 * `Steps.domain` が存在して解決できない場合でも、`Steps.lane` へはfallbackしません。
 * `Steps.lane` は legacy-compatible な layout-only 配置であり、`Steps.domain` が空の場合だけ使われます。
-* Domain group coloring は解決されたローカル `## Domains` にのみ適用されます。外部 Domain Source に基づく group coloring は後続stepです。
 * Business Flow のStep node色は引き続き `target=app_process` と `Steps.kind` を使います。
 
 #### Stepsを基本フローとして使う
diff --git a/main.js b/main.js
index 4710c97..a085d37 100644
--- a/main.js
+++ b/main.js
@@ -249,6 +249,9 @@ function formatAppProcessUnknownDomainMessage(stepId, domainId) {
 function formatAppProcessUnknownLocalDomainMessage(stepId, domainId) {
   return `app_process Step "${stepId}" references unknown local Domain "${domainId}".`;
 }
+function formatAppProcessLocalDomainFieldOverrideMessage(id, field) {
+  return `app_process local Domain "${id}" overrides external Domain ${field}.`;
+}
 
 // src/core/reference-resolver.ts
 function normalizeReferenceTarget(reference) {
@@ -824,6 +827,7 @@ function createMergeWarning(path2, message, severity) {
 }
 
 // src/core/app-process-domain-resolver.ts
+var APP_PROCESS_DOMAIN_CONFLICT_FIELDS = ["parent", "kind", "name"];
 function resolveAppProcessDomainPlacement(process, index) {
   const localDomains = process.domains ?? [];
   const hasLocalDomains = localDomains.length > 0;
@@ -843,13 +847,21 @@ function resolveAppProcessDomainPlacement(process, index) {
     conflicts: [],
     warnings: []
   };
-  const domainsById = new Map(localDomains.map((domain) => [domain.id, domain]));
-  for (const domain of resolvedSources.domains) {
-    if (!domainsById.has(domain.id)) {
-      domainsById.set(domain.id, domain);
-    }
-  }
-  const warnings = [...resolvedSources.warnings];
+  const mergeResult = mergeAppProcessDomains(
+    resolvedSources.domains,
+    localDomains,
+    process.path
+  );
+  const domainsById = new Map(mergeResult.domains.map((domain) => [domain.id, domain]));
+  const warnings = [
+    ...resolvedSources.warnings,
+    ...mergeResult.warnings,
+    ...validateMergedAppProcessDomainParents(process.path, mergeResult.domains)
+  ];
+  const conflicts = [
+    ...resolvedSources.conflicts,
+    ...mergeResult.conflicts
+  ];
   const placements = (process.steps ?? []).map((step) => {
     const domainId = step.domain?.trim() ?? "";
     if (!domainId) {
@@ -859,7 +871,7 @@ function resolveAppProcessDomainPlacement(process, index) {
     if (!domain) {
       warnings.push({
         code: "unresolved-reference",
-        message: hasLocalDomains ? formatAppProcessUnknownLocalDomainMessage(step.id, domainId) : formatAppProcessUnknownDomainMessage(step.id, domainId),
+        message: hasLocalDomains && process.domainSources.length === 0 ? formatAppProcessUnknownLocalDomainMessage(step.id, domainId) : formatAppProcessUnknownDomainMessage(step.id, domainId),
         severity: "warning",
         path: process.path,
         field: "Steps.domain",
@@ -879,13 +891,81 @@ function resolveAppProcessDomainPlacement(process, index) {
   );
   return {
     process,
-    domains: [...domainsById.values()],
+    domains: mergeResult.domains,
     sourceSummaries: resolvedSources.sourceSummaries,
-    conflicts: resolvedSources.conflicts,
+    conflicts,
     placements,
     warnings
   };
 }
+function validateMergedAppProcessDomainParents(processPath, domains) {
+  const domainIds = new Set(domains.map((domain) => domain.id));
+  const warnings = [];
+  for (const domain of domains) {
+    if (!domain.parent || domain.parent === domain.id || domainIds.has(domain.parent)) {
+      continue;
+    }
+    warnings.push({
+      code: "unresolved-reference",
+      message: formatDomainParentUnknownMessage(domain.parent),
+      severity: "warning",
+      path: processPath,
+      field: "Domains.parent",
+      context: { rowIndex: domain.rowIndex + 1 }
+    });
+  }
+  return warnings;
+}
+function mergeAppProcessDomains(externalDomains, localDomains, processPath) {
+  const domainsById = /* @__PURE__ */ new Map();
+  const order = [];
+  const conflicts = [];
+  const warnings = [];
+  for (const domain of externalDomains) {
+    if (!domainsById.has(domain.id)) {
+      order.push(domain.id);
+    }
+    domainsById.set(domain.id, { ...domain });
+  }
+  for (const localDomain of localDomains) {
+    const externalDomain = domainsById.get(localDomain.id);
+    if (!externalDomain) {
+      order.push(localDomain.id);
+      domainsById.set(localDomain.id, { ...localDomain });
+      continue;
+    }
+    for (const field of APP_PROCESS_DOMAIN_CONFLICT_FIELDS) {
+      const externalValue = externalDomain[field]?.trim() ?? "";
+      const localValue = localDomain[field]?.trim() ?? "";
+      if (externalValue === localValue) {
+        continue;
+      }
+      conflicts.push({
+        domainId: localDomain.id,
+        field,
+        earlierSourcePath: "Domain Sources",
+        laterSourcePath: processPath,
+        earlierValue: externalValue,
+        laterValue: localValue,
+        effectiveSourcePath: processPath,
+        severity: "warning"
+      });
+      warnings.push({
+        code: "invalid-structure",
+        message: formatAppProcessLocalDomainFieldOverrideMessage(localDomain.id, field),
+        severity: "warning",
+        path: processPath,
+        field: "Domains"
+      });
+    }
+    domainsById.set(localDomain.id, { ...localDomain });
+  }
+  return {
+    domains: order.map((id) => domainsById.get(id)).filter((domain) => Boolean(domain)),
+    conflicts,
+    warnings
+  };
+}
 
 // src/core/color-scheme.ts
 var BUILT_IN_COLOR_ENTRIES = [
@@ -2204,6 +2284,7 @@ function localizeDiagnosticMessage(message, language) {
     [/^Step "([^"]+)" has both domain and lane\. domain is used and lane is ignored\.$/, (_match, step) => `Step "${step}" \u306B\u306F domain \u3068 lane \u306E\u4E21\u65B9\u304C\u3042\u308A\u307E\u3059\u3002domain \u304C\u4F7F\u308F\u308C\u3001lane \u306F\u7121\u8996\u3055\u308C\u307E\u3059\u3002`],
     [/^app_process Step "([^"]+)" references unknown Domain "([^"]+)"\.$/, (_match, step, domain) => `app_process Step "${step}" \u304C\u672A\u5B9A\u7FA9\u306E Domain "${domain}" \u3092\u53C2\u7167\u3057\u3066\u3044\u307E\u3059\u3002`],
     [/^app_process Step "([^"]+)" references unknown local Domain "([^"]+)"\.$/, (_match, step, domain) => `app_process Step "${step}" \u304C\u672A\u5B9A\u7FA9\u306E\u30ED\u30FC\u30AB\u30EB Domain "${domain}" \u3092\u53C2\u7167\u3057\u3066\u3044\u307E\u3059\u3002`],
+    [/^app_process local Domain "([^"]+)" overrides external Domain (name|kind|parent)\.$/, (_match, domain, field) => `app_process \u30ED\u30FC\u30AB\u30EB Domain "${domain}" \u304C\u5916\u90E8 Domain \u306E ${field} \u3092\u4E0A\u66F8\u304D\u3057\u3066\u3044\u307E\u3059\u3002`],
     [/^(.+) "([^"]+)" could not be resolved\. Check the ID or file name\.$/, (_match, target, value) => `${target} "${value}" \u306E\u53C2\u7167\u5148\u304C\u898B\u3064\u304B\u308A\u307E\u305B\u3093\u3002ID\u307E\u305F\u306F\u30D5\u30A1\u30A4\u30EB\u540D\u3092\u78BA\u8A8D\u3057\u3066\u304F\u3060\u3055\u3044\u3002`],
     [/^unresolved (.+) "([^"]+)"$/, (_match, target, value) => `${target} "${value}" \u306E\u53C2\u7167\u5148\u304C\u898B\u3064\u304B\u308A\u307E\u305B\u3093\u3002ID\u307E\u305F\u306F\u30D5\u30A1\u30A4\u30EB\u540D\u3092\u78BA\u8A8D\u3057\u3066\u304F\u3060\u3055\u3044\u3002`],
     [/^unresolved member ref: (.+) in (.+)$/, (_match, member, owner) => `member ref "${member}" \u304C "${owner}" \u5185\u3067\u898B\u3064\u304B\u308A\u307E\u305B\u3093\u3002`],
@@ -9938,7 +10019,7 @@ function parseDomainEntries(lines, path2) {
   });
   return { rows, warnings };
 }
-function validateDomainEntries(path2, domains) {
+function validateDomainEntries(path2, domains, options = {}) {
   const warnings = [];
   const domainIds = new Set(domains.map((domain) => domain.id));
   for (const domain of domains) {
@@ -9956,7 +10037,7 @@ function validateDomainEntries(path2, domains) {
       });
       continue;
     }
-    if (!domainIds.has(domain.parent)) {
+    if (!domainIds.has(domain.parent) && !options.skipUnknownParents) {
       warnings.push({
         code: "unresolved-reference",
         message: formatDomainParentUnknownMessage(domain.parent),
@@ -10780,7 +10861,9 @@ function parseAppProcessFile(markdown, path2) {
     ...triggersTable.warnings,
     ...transitionsTable.warnings,
     ...domainsTable.warnings,
-    ...validateDomainEntries(path2, domainsTable.rows),
+    ...validateDomainEntries(path2, domainsTable.rows, {
+      skipUnknownParents: domainSourcesTable.rows.length > 0
+    }),
     ...stepsTable.warnings,
     ...flowsTable.warnings,
     ...domainSourcesTable.warnings
@@ -21294,7 +21377,7 @@ var ModelWeavePlugin = class extends import_obsidian8.Plugin {
               steps: model.steps ?? [],
               flows: model.flows ?? [],
               hasExplicitFlows: Boolean(model.hasExplicitFlows),
-              domains: model.domains
+              domains: domainPlacement.domains.length > 0 ? domainPlacement.domains : model.domains
             } : void 0,
             colorScheme: colorSchemeResult.colorScheme,
             warnings: diagnostics,
diff --git a/src/core/app-process-domain-resolver.ts b/src/core/app-process-domain-resolver.ts
index a603f64..be7a202 100644
--- a/src/core/app-process-domain-resolver.ts
+++ b/src/core/app-process-domain-resolver.ts
@@ -1,4 +1,6 @@
 import {
+  formatDomainParentUnknownMessage,
+  formatAppProcessLocalDomainFieldOverrideMessage,
   formatAppProcessUnknownDomainMessage,
   formatAppProcessUnknownLocalDomainMessage
 } from "./domain-diagnostics";
@@ -6,10 +8,14 @@ import { resolveDomainSources } from "./domain-diagram-resolver";
 import type { ModelingVaultIndex } from "./vault-index";
 import type {
   AppProcessModel,
+  DomainEntry,
+  DomainMergeConflict,
   ResolvedAppProcessDomainPlacement,
   ValidationWarning
 } from "../types/models";
 
+const APP_PROCESS_DOMAIN_CONFLICT_FIELDS = ["parent", "kind", "name"] as const;
+
 export function resolveAppProcessDomainPlacement(
   process: AppProcessModel,
   index: ModelingVaultIndex
@@ -35,13 +41,21 @@ export function resolveAppProcessDomainPlacement(
         conflicts: [],
         warnings: []
       };
-  const domainsById = new Map(localDomains.map((domain) => [domain.id, domain]));
-  for (const domain of resolvedSources.domains) {
-    if (!domainsById.has(domain.id)) {
-      domainsById.set(domain.id, domain);
-    }
-  }
-  const warnings: ValidationWarning[] = [...resolvedSources.warnings];
+  const mergeResult = mergeAppProcessDomains(
+    resolvedSources.domains,
+    localDomains,
+    process.path
+  );
+  const domainsById = new Map(mergeResult.domains.map((domain) => [domain.id, domain]));
+  const warnings: ValidationWarning[] = [
+    ...resolvedSources.warnings,
+    ...mergeResult.warnings,
+    ...validateMergedAppProcessDomainParents(process.path, mergeResult.domains)
+  ];
+  const conflicts = [
+    ...resolvedSources.conflicts,
+    ...mergeResult.conflicts
+  ];
   const placements = (process.steps ?? [])
     .map((step) => {
       const domainId = step.domain?.trim() ?? "";
@@ -53,7 +67,7 @@ export function resolveAppProcessDomainPlacement(
       if (!domain) {
         warnings.push({
           code: "unresolved-reference",
-          message: hasLocalDomains
+          message: hasLocalDomains && process.domainSources.length === 0
             ? formatAppProcessUnknownLocalDomainMessage(step.id, domainId)
             : formatAppProcessUnknownDomainMessage(step.id, domainId),
           severity: "warning",
@@ -78,10 +92,102 @@ export function resolveAppProcessDomainPlacement(
 
   return {
     process,
-    domains: [...domainsById.values()],
+    domains: mergeResult.domains,
     sourceSummaries: resolvedSources.sourceSummaries,
-    conflicts: resolvedSources.conflicts,
+    conflicts,
     placements,
     warnings
   };
 }
+
+function validateMergedAppProcessDomainParents(
+  processPath: string,
+  domains: DomainEntry[]
+): ValidationWarning[] {
+  const domainIds = new Set(domains.map((domain) => domain.id));
+  const warnings: ValidationWarning[] = [];
+
+  for (const domain of domains) {
+    if (!domain.parent || domain.parent === domain.id || domainIds.has(domain.parent)) {
+      continue;
+    }
+
+    warnings.push({
+      code: "unresolved-reference",
+      message: formatDomainParentUnknownMessage(domain.parent),
+      severity: "warning",
+      path: processPath,
+      field: "Domains.parent",
+      context: { rowIndex: domain.rowIndex + 1 }
+    });
+  }
+
+  return warnings;
+}
+
+function mergeAppProcessDomains(
+  externalDomains: DomainEntry[],
+  localDomains: DomainEntry[],
+  processPath: string
+): {
+  domains: DomainEntry[];
+  conflicts: DomainMergeConflict[];
+  warnings: ValidationWarning[];
+} {
+  const domainsById = new Map<string, DomainEntry>();
+  const order: string[] = [];
+  const conflicts: DomainMergeConflict[] = [];
+  const warnings: ValidationWarning[] = [];
+
+  for (const domain of externalDomains) {
+    if (!domainsById.has(domain.id)) {
+      order.push(domain.id);
+    }
+    domainsById.set(domain.id, { ...domain });
+  }
+
+  for (const localDomain of localDomains) {
+    const externalDomain = domainsById.get(localDomain.id);
+    if (!externalDomain) {
+      order.push(localDomain.id);
+      domainsById.set(localDomain.id, { ...localDomain });
+      continue;
+    }
+
+    for (const field of APP_PROCESS_DOMAIN_CONFLICT_FIELDS) {
+      const externalValue = externalDomain[field]?.trim() ?? "";
+      const localValue = localDomain[field]?.trim() ?? "";
+      if (externalValue === localValue) {
+        continue;
+      }
+
+      conflicts.push({
+        domainId: localDomain.id,
+        field,
+        earlierSourcePath: "Domain Sources",
+        laterSourcePath: processPath,
+        earlierValue: externalValue,
+        laterValue: localValue,
+        effectiveSourcePath: processPath,
+        severity: "warning"
+      });
+      warnings.push({
+        code: "invalid-structure",
+        message: formatAppProcessLocalDomainFieldOverrideMessage(localDomain.id, field),
+        severity: "warning",
+        path: processPath,
+        field: "Domains"
+      });
+    }
+
+    domainsById.set(localDomain.id, { ...localDomain });
+  }
+
+  return {
+    domains: order
+      .map((id) => domainsById.get(id))
+      .filter((domain): domain is DomainEntry => Boolean(domain)),
+    conflicts,
+    warnings
+  };
+}
diff --git a/src/core/current-file-diagnostics.ts b/src/core/current-file-diagnostics.ts
index ae96228..3eb9288 100644
--- a/src/core/current-file-diagnostics.ts
+++ b/src/core/current-file-diagnostics.ts
@@ -1204,6 +1204,7 @@ export function localizeDiagnosticMessage(message: string, language?: string): s
     [/^Step "([^"]+)" has both domain and lane\. domain is used and lane is ignored\.$/, (_match, step) => `Step "${step}" には domain と lane の両方があります。domain が使われ、lane は無視されます。`],
     [/^app_process Step "([^"]+)" references unknown Domain "([^"]+)"\.$/, (_match, step, domain) => `app_process Step "${step}" が未定義の Domain "${domain}" を参照しています。`],
     [/^app_process Step "([^"]+)" references unknown local Domain "([^"]+)"\.$/, (_match, step, domain) => `app_process Step "${step}" が未定義のローカル Domain "${domain}" を参照しています。`],
+    [/^app_process local Domain "([^"]+)" overrides external Domain (name|kind|parent)\.$/, (_match, domain, field) => `app_process ローカル Domain "${domain}" が外部 Domain の ${field} を上書きしています。`],
     [/^(.+) "([^"]+)" could not be resolved\. Check the ID or file name\.$/, (_match, target, value) => `${target} "${value}" の参照先が見つかりません。IDまたはファイル名を確認してください。`],
     [/^unresolved (.+) "([^"]+)"$/, (_match, target, value) => `${target} "${value}" の参照先が見つかりません。IDまたはファイル名を確認してください。`],
     [/^unresolved member ref: (.+) in (.+)$/, (_match, member, owner) => `member ref "${member}" が "${owner}" 内で見つかりません。`],
diff --git a/src/core/domain-diagnostics.ts b/src/core/domain-diagnostics.ts
index 3e5846c..a9a4792 100644
--- a/src/core/domain-diagnostics.ts
+++ b/src/core/domain-diagnostics.ts
@@ -109,3 +109,10 @@ export function formatAppProcessUnknownLocalDomainMessage(
 ): string {
   return `app_process Step "${stepId}" references unknown local Domain "${domainId}".`;
 }
+
+export function formatAppProcessLocalDomainFieldOverrideMessage(
+  id: string,
+  field: "name" | "kind" | "parent"
+): string {
+  return `app_process local Domain "${id}" overrides external Domain ${field}.`;
+}
diff --git a/src/main.ts b/src/main.ts
index 1a2c090..0c6e989 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1332,7 +1332,9 @@ export default class ModelWeavePlugin extends Plugin {
                         steps: model.steps ?? [],
                         flows: model.flows ?? [],
                         hasExplicitFlows: Boolean(model.hasExplicitFlows),
-                        domains: model.domains
+                        domains: domainPlacement.domains.length > 0
+                          ? domainPlacement.domains
+                          : model.domains
                       }
                     : undefined,
               colorScheme: colorSchemeResult.colorScheme,
diff --git a/src/parsers/app-process-parser.ts b/src/parsers/app-process-parser.ts
index a5a7cee..da47c7c 100644
--- a/src/parsers/app-process-parser.ts
+++ b/src/parsers/app-process-parser.ts
@@ -107,7 +107,9 @@ export function parseAppProcessFile(
     ...triggersTable.warnings,
     ...transitionsTable.warnings,
     ...domainsTable.warnings,
-    ...validateDomainEntries(path, domainsTable.rows),
+    ...validateDomainEntries(path, domainsTable.rows, {
+      skipUnknownParents: domainSourcesTable.rows.length > 0
+    }),
     ...stepsTable.warnings,
     ...flowsTable.warnings,
     ...domainSourcesTable.warnings
diff --git a/src/parsers/domains-parser.ts b/src/parsers/domains-parser.ts
index a80af85..8013450 100644
--- a/src/parsers/domains-parser.ts
+++ b/src/parsers/domains-parser.ts
@@ -123,7 +123,8 @@ export function parseDomainEntries(
 
 export function validateDomainEntries(
   path: string,
-  domains: DomainEntry[]
+  domains: DomainEntry[],
+  options: { skipUnknownParents?: boolean } = {}
 ): ValidationWarning[] {
   const warnings: ValidationWarning[] = [];
   const domainIds = new Set(domains.map((domain) => domain.id));
@@ -145,7 +146,7 @@ export function validateDomainEntries(
       continue;
     }
 
-    if (!domainIds.has(domain.parent)) {
+    if (!domainIds.has(domain.parent) && !options.skipUnknownParents) {
       warnings.push({
         code: "unresolved-reference",
         message: formatDomainParentUnknownMessage(domain.parent),
diff --git a/test/app-process-domain-placement.test.mjs b/test/app-process-domain-placement.test.mjs
index af806b1..13b633d 100644
--- a/test/app-process-domain-placement.test.mjs
+++ b/test/app-process-domain-placement.test.mjs
@@ -699,9 +699,322 @@ test("app_process Domain Sources resolve known step domains", () => {
   assert.equal(resolved.placements[0].status, "resolved");
   assert.equal(resolved.placements[0].domain.name, "Fulfillment");
   assert.equal(resolved.placements[0].domain.kind, "business_domain");
+  assert.equal(resolved.domains[0].id, "fulfillment");
   assert.equal(resolved.warnings.length, 0);
 });
 
+test("app_process Domain Sources render merged hierarchy", () => {
+  const { index, model } = buildIndexWithProcess(
+    processMarkdown(
+      domainStepsHeader,
+      [
+        "| receive | office | Receive order | process |  |  |  |  |  | external child |",
+        "| open | wms | Open WMS | screen |  |  |  |  |  | external grandchild |"
+      ].join("\n"),
+      [
+        "## Domain Sources",
+        "",
+        "| ref |",
+        "|---|",
+        "| [[DOMAINS-COMPANY]] |"
+      ].join("\n")
+    ),
+    [
+      {
+        path: "DOMAINS-COMPANY.md",
+        content: domainsMarkdown([
+          "| warehouse | Warehouse | operations | | Warehouse area |",
+          "| office | Office | organization | warehouse | Office area |",
+          "| wms | WMS | system | office | Warehouse management system |"
+        ].join("\n"))
+      }
+    ]
+  );
+
+  const resolved = resolveAppProcessDomainPlacement(model, index);
+  const source = buildAppProcessBusinessFlowMermaidSource({
+    title: model.name,
+    hasExplicitFlows: false,
+    domains: resolved.domains,
+    steps: model.steps,
+    flows: []
+  });
+
+  assert.equal(resolved.warnings.length, 0);
+  assert.match(source, /subgraph domain_warehouse\["Warehouse"\]/);
+  assert.match(source, /subgraph domain_office\["Office"\]/);
+  assert.match(source, /subgraph domain_wms\["WMS"\]/);
+  assert.match(source, /S1\["Receive order"\]/);
+  assert.match(source, /S2\[\/"Open WMS"\/\]/);
+});
+
+test("app_process mixed local and external Domain Sources render full Business Flow hierarchy", () => {
+  const processContent = `---
+type: app_process
+id: PROC-DOMAIN-PLACEMENT
+name: Domain Placement
+---
+
+# Domain Placement
+
+## Domain Sources
+
+| ref |
+|---|
+| [[DOMAINS-COMPANY]] |
+
+${localDomainsSection([
+  "| office | 事務所 | organization | warehouse | local definition override |",
+  "| qa | 検品 | operations | floor | local child of external floor |"
+].join("\n"))}
+
+## Steps
+
+${domainStepsHeader}
+| start | office | 在庫照会開始 | start |  |  |  |  |  |  |
+| open | wms | 在庫照会画面を開く | screen |  |  |  |  |  |  |
+| search | wms | 在庫検索 | input |  |  |  |  |  |  |
+| judge | office | 在庫有無を判定 | decision |  |  |  |  |  |  |
+| available | floor | 在庫ありの場合受注 | subflow |  |  |  |  |  |  |
+| inspect | qa | 検品対象を確認 | process |  |  |  |  |  | local Domainsで追加した領域 |
+| unavailable | external | 在庫なしの場合は連絡 | subflow |  |  |  |  |  |  |
+| end |  | 終了 | end |  |  |  |  |  |  |
+
+## Flows
+
+| from | to | condition | label | notes |
+|---|---|---|---|---|
+| start | open |  |  |  |
+| open | search |  |  |  |
+| search | judge |  |  |  |
+| judge | available |  | 在庫あり |  |
+| judge | unavailable |  | 在庫なし |  |
+| available | inspect |  |  |  |
+| inspect | end |  |  |  |
+| unavailable | end |  |  |  |
+`;
+  const parsed = parseAppProcessFile(processContent, "PROC-DOMAIN-PLACEMENT.md");
+  assert.ok(parsed.file);
+  assert.equal(
+    parsed.warnings.some((warning) =>
+      warning.message === 'Domain parent "floor" is not defined.'
+    ),
+    false
+  );
+
+  const { index, model } = buildIndexWithProcess(
+    processContent,
+    [
+      {
+        path: "DOMAINS-COMPANY.md",
+        content: domainsMarkdown([
+          "| warehouse | 倉庫 | operations | | |",
+          "| office | 事務所 | organization | warehouse | |",
+          "| wms | WMS | system | office | |",
+          "| floor | フロア | location | warehouse | |",
+          "| external | 外部 | external | | |"
+        ].join("\n"))
+      }
+    ]
+  );
+  const resolved = resolveAppProcessDomainPlacement(model, index);
+  const scheme = {
+    id: "test",
+    name: "Test",
+    entries: [
+      { target: "domain", kind: "operations", fill: "#111111", stroke: "#222222", text: "#ffffff", rowIndex: 0 },
+      { target: "domain", kind: "organization", fill: "#333333", stroke: "#444444", text: "#eeeeee", rowIndex: 1 },
+      { target: "domain", kind: "system", fill: "#555555", stroke: "#666666", text: "#ffffff", rowIndex: 2 },
+      { target: "domain", kind: "location", fill: "#777777", stroke: "#888888", text: "#ffffff", rowIndex: 3 },
+      { target: "domain", kind: "external", fill: "#999999", stroke: "#aaaaaa", text: "#111111", rowIndex: 4 },
+      { target: "app_process", kind: "process", fill: "#e8f5e9", stroke: "#388e3c", text: "#111111", rowIndex: 5 },
+      { kind: "default", fill: "#f5f5f5", stroke: "#9e9e9e", text: "#111111", rowIndex: 6 }
+    ],
+    defaultStyle: {
+      fill: "#f5f5f5",
+      stroke: "#9e9e9e",
+      text: "#111111"
+    }
+  };
+  const source = buildAppProcessBusinessFlowMermaidSource({
+    title: model.name,
+    hasExplicitFlows: Boolean(model.hasExplicitFlows),
+    domains: resolved.domains,
+    steps: model.steps,
+    flows: model.flows
+  }, scheme);
+
+  assert.equal(
+    resolved.warnings.some((warning) =>
+      warning.message === 'Domain parent "floor" is not defined.'
+    ),
+    false
+  );
+  assert.equal(resolved.placements.filter((placement) => placement.status === "resolved").length, 7);
+  assert.match(source, /subgraph domain_warehouse\["倉庫"\]/);
+  assert.match(source, /subgraph domain_office\["事務所"\]/);
+  assert.match(source, /subgraph domain_wms\["WMS"\]/);
+  assert.match(source, /subgraph domain_floor\["フロア"\]/);
+  assert.match(source, /subgraph domain_qa\["検品"\]/);
+  assert.match(source, /subgraph domain_external\["外部"\]/);
+  assert.ok(source.indexOf('subgraph domain_wms["WMS"]') > source.indexOf('subgraph domain_office["事務所"]'));
+  assert.ok(source.indexOf('subgraph domain_qa["検品"]') > source.indexOf('subgraph domain_floor["フロア"]'));
+  assert.match(source, /style domain_warehouse fill:#111111,stroke:#222222,color:#ffffff/);
+  assert.match(source, /style domain_wms fill:#555555,stroke:#666666,color:#ffffff/);
+  assert.match(source, /style domain_floor fill:#777777,stroke:#888888,color:#ffffff/);
+  assert.match(source, /style domain_external fill:#999999,stroke:#aaaaaa,color:#111111/);
+  assert.match(source, /classDef kind_app_process_process fill:#e8f5e9,stroke:#388e3c,color:#111111/);
+  assert.match(source, /S4 -->\|"在庫あり"\| S5/);
+  assert.match(source, /S4 -->\|"在庫なし"\| S7/);
+});
+
+test("app_process Domain group Color Scheme uses merged external Domain kind", () => {
+  const { index, model } = buildIndexWithProcess(
+    processMarkdown(
+      domainStepsHeader,
+      "| receive | fulfillment | Receive order | process |  |  |  |  |  | external color |",
+      [
+        "## Domain Sources",
+        "",
+        "| ref |",
+        "|---|",
+        "| [[DOMAINS-COMPANY]] |"
+      ].join("\n")
+    ),
+    [
+      {
+        path: "DOMAINS-COMPANY.md",
+        content: domainsMarkdown(
+          "| fulfillment | Fulfillment | business_domain | | Fulfillment process area |"
+        )
+      }
+    ]
+  );
+  const resolved = resolveAppProcessDomainPlacement(model, index);
+  const scheme = {
+    id: "test",
+    name: "Test",
+    entries: [
+      { target: "domain", kind: "business_domain", fill: "#123456", stroke: "#234567", text: "#ffffff", rowIndex: 0 },
+      { target: "app_process", kind: "process", fill: "#e8f5e9", stroke: "#388e3c", text: "#111111", rowIndex: 1 },
+      { kind: "default", fill: "#f5f5f5", stroke: "#9e9e9e", text: "#111111", rowIndex: 2 }
+    ],
+    defaultStyle: {
+      fill: "#f5f5f5",
+      stroke: "#9e9e9e",
+      text: "#111111"
+    }
+  };
+  const source = buildAppProcessBusinessFlowMermaidSource({
+    title: model.name,
+    hasExplicitFlows: false,
+    domains: resolved.domains,
+    steps: model.steps,
+    flows: []
+  }, scheme);
+
+  assert.match(source, /style domain_fulfillment fill:#123456,stroke:#234567,color:#ffffff/);
+  assert.match(source, /classDef kind_app_process_process fill:#e8f5e9,stroke:#388e3c,color:#111111/);
+});
+
+test("app_process local Domains override external source definitions", () => {
+  const { index, model } = buildIndexWithProcess(
+    processMarkdown(
+      domainStepsHeader,
+      "| receive | fulfillment | Receive order | process |  |  |  |  |  | local override |",
+      [
+        "## Domain Sources",
+        "",
+        "| ref |",
+        "|---|",
+        "| [[DOMAINS-COMPANY]] |",
+        "",
+        localDomainsSection(
+          "| fulfillment | Local Fulfillment | local_kind | local_parent | Local definition |"
+        )
+      ].join("\n")
+    ),
+    [
+      {
+        path: "DOMAINS-COMPANY.md",
+        content: domainsMarkdown(
+          "| fulfillment | External Fulfillment | external_kind | external_parent | External definition |"
+        )
+      }
+    ]
+  );
+
+  const resolved = resolveAppProcessDomainPlacement(model, index);
+  const domain = resolved.placements[0].domain;
+  const messages = resolved.warnings.map((warning) => warning.message);
+
+  assert.equal(domain.name, "Local Fulfillment");
+  assert.equal(domain.kind, "local_kind");
+  assert.equal(domain.parent, "local_parent");
+  assert.ok(messages.includes('app_process local Domain "fulfillment" overrides external Domain name.'));
+  assert.ok(messages.includes('app_process local Domain "fulfillment" overrides external Domain kind.'));
+  assert.ok(messages.includes('app_process local Domain "fulfillment" overrides external Domain parent.'));
+  assert.equal(resolved.conflicts.length, 3);
+  assert.equal(
+    localizeDiagnosticMessage(messages[0], "ja"),
+    'app_process ローカル Domain "fulfillment" が外部 Domain の parent を上書きしています。'
+  );
+});
+
+test("app_process local override controls rendered Domain color", () => {
+  const { index, model } = buildIndexWithProcess(
+    processMarkdown(
+      domainStepsHeader,
+      "| receive | fulfillment | Receive order | process |  |  |  |  |  | local color override |",
+      [
+        "## Domain Sources",
+        "",
+        "| ref |",
+        "|---|",
+        "| [[DOMAINS-COMPANY]] |",
+        "",
+        localDomainsSection(
+          "| fulfillment | Local Fulfillment | local_kind | | Local definition |"
+        )
+      ].join("\n")
+    ),
+    [
+      {
+        path: "DOMAINS-COMPANY.md",
+        content: domainsMarkdown(
+          "| fulfillment | External Fulfillment | external_kind | | External definition |"
+        )
+      }
+    ]
+  );
+  const resolved = resolveAppProcessDomainPlacement(model, index);
+  const scheme = {
+    id: "test",
+    name: "Test",
+    entries: [
+      { target: "domain", kind: "external_kind", fill: "#000000", stroke: "#000000", text: "#ffffff", rowIndex: 0 },
+      { target: "domain", kind: "local_kind", fill: "#abcdef", stroke: "#123456", text: "#111111", rowIndex: 1 },
+      { kind: "default", fill: "#f5f5f5", stroke: "#9e9e9e", text: "#111111", rowIndex: 2 }
+    ],
+    defaultStyle: {
+      fill: "#f5f5f5",
+      stroke: "#9e9e9e",
+      text: "#111111"
+    }
+  };
+  const source = buildAppProcessBusinessFlowMermaidSource({
+    title: model.name,
+    hasExplicitFlows: false,
+    domains: resolved.domains,
+    steps: model.steps,
+    flows: []
+  }, scheme);
+
+  assert.match(source, /subgraph domain_fulfillment\["Local Fulfillment"\]/);
+  assert.match(source, /style domain_fulfillment fill:#abcdef,stroke:#123456,color:#111111/);
+  assert.doesNotMatch(source, /fill:#000000,stroke:#000000,color:#ffffff/);
+});
+
 test("app_process unknown step domain warns when Domain Sources are present", () => {
   const { index, model } = buildIndexWithProcess(
     processMarkdown(