diff --git a/packages/cli/src/config/settings-validation.test.ts b/packages/cli/src/config/settings-validation.test.ts
index baf9b5bbdb..e6f920e44b 100644
--- a/packages/cli/src/config/settings-validation.test.ts
+++ b/packages/cli/src/config/settings-validation.test.ts
@@ -298,6 +298,33 @@ describe('settings-validation', () => {
         expect(issue).toBeDefined();
       }
     });
+
+    it('should accept customThemes with text.response color override', () => {
+      // Regression test for #25610: `response` is a documented and
+      // implemented color override for model responses (see
+      // packages/cli/src/ui/themes/theme.ts and semantic-tokens.ts),
+      // but was missing from the CustomTheme validation schema.
+      const validSettings = {
+        ui: {
+          theme: 'LimeWhite',
+          customThemes: {
+            LimeWhite: {
+              type: 'custom',
+              name: 'LimeWhite',
+              text: {
+                primary: '#00FF00',
+                response: '#FFFFFF',
+                secondary: '#a0a0a0',
+                accent: '#00FF00',
+              },
+            },
+          },
+        },
+      };
+
+      const result = validateSettings(validSettings);
+      expect(result.success).toBe(true);
+    });
   });
 
   describe('formatValidationError', () => {
diff --git a/packages/cli/src/config/settingsSchema.ts b/packages/cli/src/config/settingsSchema.ts
index 08edbd66f9..cea336a40d 100644
--- a/packages/cli/src/config/settingsSchema.ts
+++ b/packages/cli/src/config/settingsSchema.ts
@@ -3278,6 +3278,7 @@ export const SETTINGS_SCHEMA_DEFINITIONS: Record<
           secondary: { type: 'string' },
           link: { type: 'string' },
           accent: { type: 'string' },
+          response: { type: 'string' },
         },
       },
       background: {
diff --git a/schemas/settings.schema.json b/schemas/settings.schema.json
index a883150d66..a3c4b8cc94 100644
--- a/schemas/settings.schema.json
+++ b/schemas/settings.schema.json
@@ -3880,6 +3880,9 @@
             },
             "accent": {
               "type": "string"
+            },
+            "response": {
+              "type": "string"
             }
           }
         },