diff --git a/package-lock.json b/package-lock.json
index 720a6534b1..82fe57f61e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -17281,6 +17281,7 @@
         "strip-ansi": "^7.1.0",
         "strip-json-comments": "^3.1.1",
         "tar": "^7.5.1",
+        "tinygradient": "^1.1.5",
         "undici": "^7.10.0",
         "wrap-ansi": "9.0.2",
         "yargs": "^17.7.2",
diff --git a/packages/cli/package.json b/packages/cli/package.json
index 956f30ed39..dc8dc52a5b 100644
--- a/packages/cli/package.json
+++ b/packages/cli/package.json
@@ -58,6 +58,7 @@
     "strip-ansi": "^7.1.0",
     "strip-json-comments": "^3.1.1",
     "tar": "^7.5.1",
+    "tinygradient": "^1.1.5",
     "undici": "^7.10.0",
     "wrap-ansi": "9.0.2",
     "yargs": "^17.7.2",
diff --git a/packages/cli/src/ui/colors.ts b/packages/cli/src/ui/colors.ts
index a20a990973..87ec04b730 100644
--- a/packages/cli/src/ui/colors.ts
+++ b/packages/cli/src/ui/colors.ts
@@ -50,6 +50,9 @@ export const Colors: ColorsTheme = {
   get Gray() {
     return themeManager.getActiveTheme().colors.Gray;
   },
+  get DarkGray() {
+    return themeManager.getActiveTheme().colors.DarkGray;
+  },
   get GradientColors() {
     return themeManager.getActiveTheme().colors.GradientColors;
   },
diff --git a/packages/cli/src/ui/themes/ansi-light.ts b/packages/cli/src/ui/themes/ansi-light.ts
index 8ccb65bd96..95807064e2 100644
--- a/packages/cli/src/ui/themes/ansi-light.ts
+++ b/packages/cli/src/ui/themes/ansi-light.ts
@@ -22,6 +22,7 @@ const ansiLightColors: ColorsTheme = {
   DiffRemoved: '#FFE5E5',
   Comment: 'gray',
   Gray: 'gray',
+  DarkGray: 'gray',
   GradientColors: ['blue', 'green'],
 };
 
diff --git a/packages/cli/src/ui/themes/ansi.ts b/packages/cli/src/ui/themes/ansi.ts
index 21644813a4..335c9abcfc 100644
--- a/packages/cli/src/ui/themes/ansi.ts
+++ b/packages/cli/src/ui/themes/ansi.ts
@@ -22,6 +22,7 @@ const ansiColors: ColorsTheme = {
   DiffRemoved: '#4D0000',
   Comment: 'gray',
   Gray: 'gray',
+  DarkGray: 'gray',
   GradientColors: ['cyan', 'green'],
 };
 
diff --git a/packages/cli/src/ui/themes/atom-one-dark.ts b/packages/cli/src/ui/themes/atom-one-dark.ts
index 5545971e09..5217a8bf30 100644
--- a/packages/cli/src/ui/themes/atom-one-dark.ts
+++ b/packages/cli/src/ui/themes/atom-one-dark.ts
@@ -5,6 +5,7 @@
  */
 
 import { type ColorsTheme, Theme } from './theme.js';
+import { interpolateColor } from './color-utils.js';
 
 const atomOneDarkColors: ColorsTheme = {
   type: 'dark',
@@ -21,6 +22,7 @@ const atomOneDarkColors: ColorsTheme = {
   DiffRemoved: '#562B2F',
   Comment: '#5c6370',
   Gray: '#5c6370',
+  DarkGray: interpolateColor('#5c6370', '#282c34', 0.5),
   GradientColors: ['#61aeee', '#98c379'],
 };
 
diff --git a/packages/cli/src/ui/themes/ayu-light.ts b/packages/cli/src/ui/themes/ayu-light.ts
index 8410cfb270..393ed44ba6 100644
--- a/packages/cli/src/ui/themes/ayu-light.ts
+++ b/packages/cli/src/ui/themes/ayu-light.ts
@@ -5,6 +5,7 @@
  */
 
 import { type ColorsTheme, Theme } from './theme.js';
+import { interpolateColor } from './color-utils.js';
 
 const ayuLightColors: ColorsTheme = {
   type: 'light',
@@ -21,6 +22,7 @@ const ayuLightColors: ColorsTheme = {
   DiffRemoved: '#FFCCCC',
   Comment: '#ABADB1',
   Gray: '#a6aaaf',
+  DarkGray: interpolateColor('#a6aaaf', '#f8f9fa', 0.5),
   GradientColors: ['#399ee6', '#86b300'],
 };
 
diff --git a/packages/cli/src/ui/themes/ayu.ts b/packages/cli/src/ui/themes/ayu.ts
index 7a3bde778d..71798aacf2 100644
--- a/packages/cli/src/ui/themes/ayu.ts
+++ b/packages/cli/src/ui/themes/ayu.ts
@@ -5,6 +5,7 @@
  */
 
 import { type ColorsTheme, Theme } from './theme.js';
+import { interpolateColor } from './color-utils.js';
 
 const ayuDarkColors: ColorsTheme = {
   type: 'dark',
@@ -21,6 +22,7 @@ const ayuDarkColors: ColorsTheme = {
   DiffRemoved: '#3D1215',
   Comment: '#646A71',
   Gray: '#3D4149',
+  DarkGray: interpolateColor('#3D4149', '#0b0e14', 0.5),
   GradientColors: ['#FFB454', '#F26D78'],
 };
 
diff --git a/packages/cli/src/ui/themes/color-utils.test.ts b/packages/cli/src/ui/themes/color-utils.test.ts
index dfb1be83c8..9d6a11698a 100644
--- a/packages/cli/src/ui/themes/color-utils.test.ts
+++ b/packages/cli/src/ui/themes/color-utils.test.ts
@@ -8,6 +8,7 @@ import { describe, it, expect } from 'vitest';
 import {
   isValidColor,
   resolveColor,
+  interpolateColor,
   CSS_NAME_TO_HEX_MAP,
   INK_SUPPORTED_NAMES,
 } from './color-utils.js';
@@ -218,4 +219,19 @@ describe('Color Utils', () => {
       }
     });
   });
+
+  describe('interpolateColor', () => {
+    it('should interpolate between two colors', () => {
+      // Midpoint between black (#000000) and white (#ffffff) should be gray
+      expect(interpolateColor('#000000', '#ffffff', 0.5)).toBe('#7f7f7f');
+    });
+
+    it('should return start color when factor is 0', () => {
+      expect(interpolateColor('#ff0000', '#0000ff', 0)).toBe('#ff0000');
+    });
+
+    it('should return end color when factor is 1', () => {
+      expect(interpolateColor('#ff0000', '#0000ff', 1)).toBe('#0000ff');
+    });
+  });
 });
diff --git a/packages/cli/src/ui/themes/color-utils.ts b/packages/cli/src/ui/themes/color-utils.ts
index 703752fd9e..1f326a4840 100644
--- a/packages/cli/src/ui/themes/color-utils.ts
+++ b/packages/cli/src/ui/themes/color-utils.ts
@@ -5,6 +5,7 @@
  */
 
 import { debugLogger } from '@google/gemini-cli-core';
+import tinygradient from 'tinygradient';
 
 // Mapping from common CSS color names (lowercase) to hex codes (lowercase)
 // Excludes names directly supported by Ink
@@ -231,3 +232,13 @@ export function resolveColor(colorValue: string): string | undefined {
   );
   return undefined;
 }
+
+export function interpolateColor(
+  color1: string,
+  color2: string,
+  factor: number,
+) {
+  const gradient = tinygradient(color1, color2);
+  const color = gradient.rgbAt(factor);
+  return color.toHexString();
+}
diff --git a/packages/cli/src/ui/themes/dracula.ts b/packages/cli/src/ui/themes/dracula.ts
index 07261d5124..2cd2802c45 100644
--- a/packages/cli/src/ui/themes/dracula.ts
+++ b/packages/cli/src/ui/themes/dracula.ts
@@ -5,6 +5,7 @@
  */
 
 import { type ColorsTheme, Theme } from './theme.js';
+import { interpolateColor } from './color-utils.js';
 
 const draculaColors: ColorsTheme = {
   type: 'dark',
@@ -21,6 +22,7 @@ const draculaColors: ColorsTheme = {
   DiffRemoved: '#6e1818',
   Comment: '#6272a4',
   Gray: '#6272a4',
+  DarkGray: interpolateColor('#6272a4', '#282a36', 0.5),
   GradientColors: ['#ff79c6', '#8be9fd'],
 };
 
diff --git a/packages/cli/src/ui/themes/github-dark.ts b/packages/cli/src/ui/themes/github-dark.ts
index 2e7b0a2eb8..28c14f598d 100644
--- a/packages/cli/src/ui/themes/github-dark.ts
+++ b/packages/cli/src/ui/themes/github-dark.ts
@@ -5,6 +5,7 @@
  */
 
 import { type ColorsTheme, Theme } from './theme.js';
+import { interpolateColor } from './color-utils.js';
 
 const githubDarkColors: ColorsTheme = {
   type: 'dark',
@@ -21,6 +22,7 @@ const githubDarkColors: ColorsTheme = {
   DiffRemoved: '#502125',
   Comment: '#6A737D',
   Gray: '#6A737D',
+  DarkGray: interpolateColor('#6A737D', '#24292e', 0.5),
   GradientColors: ['#79B8FF', '#85E89D'],
 };
 
diff --git a/packages/cli/src/ui/themes/github-light.ts b/packages/cli/src/ui/themes/github-light.ts
index dcb4bbf006..264a9d7a88 100644
--- a/packages/cli/src/ui/themes/github-light.ts
+++ b/packages/cli/src/ui/themes/github-light.ts
@@ -5,6 +5,7 @@
  */
 
 import { type ColorsTheme, Theme } from './theme.js';
+import { interpolateColor } from './color-utils.js';
 
 const githubLightColors: ColorsTheme = {
   type: 'light',
@@ -21,6 +22,7 @@ const githubLightColors: ColorsTheme = {
   DiffRemoved: '#FFCCCC',
   Comment: '#998',
   Gray: '#999',
+  DarkGray: interpolateColor('#999', '#f8f8f8', 0.5),
   GradientColors: ['#458', '#008080'],
 };
 
diff --git a/packages/cli/src/ui/themes/googlecode.ts b/packages/cli/src/ui/themes/googlecode.ts
index 27fd50e9af..1795451c91 100644
--- a/packages/cli/src/ui/themes/googlecode.ts
+++ b/packages/cli/src/ui/themes/googlecode.ts
@@ -5,6 +5,7 @@
  */
 
 import { type ColorsTheme, Theme, lightTheme } from './theme.js';
+import { interpolateColor } from './color-utils.js';
 
 const googleCodeColors: ColorsTheme = {
   type: 'light',
@@ -21,6 +22,7 @@ const googleCodeColors: ColorsTheme = {
   DiffRemoved: '#FEDEDE',
   Comment: '#5f6368',
   Gray: lightTheme.Gray,
+  DarkGray: interpolateColor(lightTheme.Gray, '#ffffff', 0.5),
   GradientColors: ['#066', '#606'],
 };
 
diff --git a/packages/cli/src/ui/themes/no-color.ts b/packages/cli/src/ui/themes/no-color.ts
index 3e5efb5f94..9accca8851 100644
--- a/packages/cli/src/ui/themes/no-color.ts
+++ b/packages/cli/src/ui/themes/no-color.ts
@@ -23,6 +23,7 @@ const noColorColorsTheme: ColorsTheme = {
   DiffRemoved: '',
   Comment: '',
   Gray: '',
+  DarkGray: '',
 };
 
 const noColorSemanticColors: SemanticColors = {
@@ -46,6 +47,7 @@ const noColorSemanticColors: SemanticColors = {
   ui: {
     comment: '',
     symbol: '',
+    dark: '',
     gradient: [],
   },
   status: {
diff --git a/packages/cli/src/ui/themes/semantic-tokens.ts b/packages/cli/src/ui/themes/semantic-tokens.ts
index 56430304e7..75059d2e0c 100644
--- a/packages/cli/src/ui/themes/semantic-tokens.ts
+++ b/packages/cli/src/ui/themes/semantic-tokens.ts
@@ -27,6 +27,7 @@ export interface SemanticColors {
   ui: {
     comment: string;
     symbol: string;
+    dark: string;
     gradient: string[] | undefined;
   };
   status: {
@@ -57,6 +58,7 @@ export const lightSemanticColors: SemanticColors = {
   ui: {
     comment: lightTheme.Comment,
     symbol: lightTheme.Gray,
+    dark: lightTheme.DarkGray,
     gradient: lightTheme.GradientColors,
   },
   status: {
@@ -87,6 +89,7 @@ export const darkSemanticColors: SemanticColors = {
   ui: {
     comment: darkTheme.Comment,
     symbol: darkTheme.Gray,
+    dark: darkTheme.DarkGray,
     gradient: darkTheme.GradientColors,
   },
   status: {
@@ -117,6 +120,7 @@ export const ansiSemanticColors: SemanticColors = {
   ui: {
     comment: ansiTheme.Comment,
     symbol: ansiTheme.Gray,
+    dark: ansiTheme.DarkGray,
     gradient: ansiTheme.GradientColors,
   },
   status: {
diff --git a/packages/cli/src/ui/themes/shades-of-purple.ts b/packages/cli/src/ui/themes/shades-of-purple.ts
index 6e20240f91..7fc513a618 100644
--- a/packages/cli/src/ui/themes/shades-of-purple.ts
+++ b/packages/cli/src/ui/themes/shades-of-purple.ts
@@ -9,6 +9,7 @@
  * @author Ahmad Awais <https://twitter.com/mrahmadawais/>
  */
 import { type ColorsTheme, Theme } from './theme.js';
+import { interpolateColor } from './color-utils.js';
 
 const shadesOfPurpleColors: ColorsTheme = {
   type: 'dark',
@@ -26,6 +27,7 @@ const shadesOfPurpleColors: ColorsTheme = {
   DiffRemoved: '#572244',
   Comment: '#B362FF', // Comment color (same as AccentPurple)
   Gray: '#726c86', // Gray color
+  DarkGray: interpolateColor('#726c86', '#2d2b57', 0.5),
   GradientColors: ['#4d21fc', '#847ace', '#ff628c'],
 };
 
diff --git a/packages/cli/src/ui/themes/theme.test.ts b/packages/cli/src/ui/themes/theme.test.ts
index 1c06181cac..8a56dd9bae 100644
--- a/packages/cli/src/ui/themes/theme.test.ts
+++ b/packages/cli/src/ui/themes/theme.test.ts
@@ -8,9 +8,80 @@ import { describe, it, expect } from 'vitest';
 import * as themeModule from './theme.js';
 import { themeManager } from './theme-manager.js';
 
-const { validateCustomTheme } = themeModule;
+const { validateCustomTheme, createCustomTheme } = themeModule;
 type CustomTheme = themeModule.CustomTheme;
 
+describe('createCustomTheme', () => {
+  const baseTheme: CustomTheme = {
+    type: 'custom',
+    name: 'Test Theme',
+    Background: '#000000',
+    Foreground: '#ffffff',
+    LightBlue: '#ADD8E6',
+    AccentBlue: '#0000FF',
+    AccentPurple: '#800080',
+    AccentCyan: '#00FFFF',
+    AccentGreen: '#008000',
+    AccentYellow: '#FFFF00',
+    AccentRed: '#FF0000',
+    DiffAdded: '#00FF00',
+    DiffRemoved: '#FF0000',
+    Comment: '#808080',
+    Gray: '#cccccc',
+    // DarkGray intentionally omitted to test fallback
+  };
+
+  it('should interpolate DarkGray when not provided', () => {
+    const theme = createCustomTheme(baseTheme);
+    // Interpolate between Gray (#cccccc) and Background (#000000) at 0.5
+    // #cccccc is RGB(204, 204, 204)
+    // #000000 is RGB(0, 0, 0)
+    // Midpoint is RGB(102, 102, 102) which is #666666
+    expect(theme.colors.DarkGray).toBe('#666666');
+  });
+
+  it('should use provided DarkGray', () => {
+    const theme = createCustomTheme({
+      ...baseTheme,
+      DarkGray: '#123456',
+    });
+    expect(theme.colors.DarkGray).toBe('#123456');
+  });
+
+  it('should interpolate DarkGray when text.secondary is provided but DarkGray is not', () => {
+    const customTheme: CustomTheme = {
+      type: 'custom',
+      name: 'Test',
+      text: {
+        secondary: '#cccccc', // Gray source
+      },
+      background: {
+        primary: '#000000', // Background source
+      },
+    };
+    const theme = createCustomTheme(customTheme);
+    // Should be interpolated between #cccccc and #000000 at 0.5 -> #666666
+    expect(theme.colors.DarkGray).toBe('#666666');
+  });
+
+  it('should prefer text.secondary over Gray for interpolation', () => {
+    const customTheme: CustomTheme = {
+      type: 'custom',
+      name: 'Test',
+      text: {
+        secondary: '#cccccc', // Should be used
+      },
+      Gray: '#aaaaaa', // Should be ignored
+      background: {
+        primary: '#000000',
+      },
+    };
+    const theme = createCustomTheme(customTheme);
+    // Interpolate between #cccccc and #000000 -> #666666
+    expect(theme.colors.DarkGray).toBe('#666666');
+  });
+});
+
 describe('validateCustomTheme', () => {
   const validTheme: CustomTheme = {
     type: 'custom',
diff --git a/packages/cli/src/ui/themes/theme.ts b/packages/cli/src/ui/themes/theme.ts
index 99a7efa6b0..5dc5cfaae4 100644
--- a/packages/cli/src/ui/themes/theme.ts
+++ b/packages/cli/src/ui/themes/theme.ts
@@ -6,7 +6,7 @@
 
 import type { CSSProperties } from 'react';
 import type { SemanticColors } from './semantic-tokens.js';
-import { resolveColor } from './color-utils.js';
+import { resolveColor, interpolateColor } from './color-utils.js';
 
 export type ThemeType = 'light' | 'dark' | 'ansi' | 'custom';
 
@@ -25,6 +25,7 @@ export interface ColorsTheme {
   DiffRemoved: string;
   Comment: string;
   Gray: string;
+  DarkGray: string;
   GradientColors?: string[];
 }
 
@@ -74,13 +75,14 @@ export interface CustomTheme {
   DiffRemoved?: string;
   Comment?: string;
   Gray?: string;
+  DarkGray?: string;
   GradientColors?: string[];
 }
 
 export const lightTheme: ColorsTheme = {
   type: 'light',
   Background: '#FAFAFA',
-  Foreground: '',
+  Foreground: '#383A42',
   LightBlue: '#89BDCD',
   AccentBlue: '#3B82F6',
   AccentPurple: '#8B5CF6',
@@ -92,13 +94,14 @@ export const lightTheme: ColorsTheme = {
   DiffRemoved: '#FFCCCC',
   Comment: '#008000',
   Gray: '#97a0b0',
+  DarkGray: interpolateColor('#97a0b0', '#FAFAFA', 0.5),
   GradientColors: ['#4796E4', '#847ACE', '#C3677F'],
 };
 
 export const darkTheme: ColorsTheme = {
   type: 'dark',
   Background: '#1E1E2E',
-  Foreground: '',
+  Foreground: '#CDD6F4',
   LightBlue: '#ADD8E6',
   AccentBlue: '#89B4FA',
   AccentPurple: '#CBA6F7',
@@ -110,6 +113,7 @@ export const darkTheme: ColorsTheme = {
   DiffRemoved: '#430000',
   Comment: '#6C7086',
   Gray: '#6C7086',
+  DarkGray: interpolateColor('#6C7086', '#1E1E2E', 0.5),
   GradientColors: ['#4796E4', '#847ACE', '#C3677F'],
 };
 
@@ -128,6 +132,7 @@ export const ansiTheme: ColorsTheme = {
   DiffRemoved: 'red',
   Comment: 'gray',
   Gray: 'gray',
+  DarkGray: 'gray',
 };
 
 export class Theme {
@@ -176,6 +181,7 @@ export class Theme {
       ui: {
         comment: this.colors.Gray,
         symbol: this.colors.AccentCyan,
+        dark: this.colors.DarkGray,
         gradient: this.colors.GradientColors,
       },
       status: {
@@ -267,6 +273,13 @@ export function createCustomTheme(customTheme: CustomTheme): Theme {
       customTheme.background?.diff?.removed ?? customTheme.DiffRemoved ?? '',
     Comment: customTheme.ui?.comment ?? customTheme.Comment ?? '',
     Gray: customTheme.text?.secondary ?? customTheme.Gray ?? '',
+    DarkGray:
+      customTheme.DarkGray ??
+      interpolateColor(
+        customTheme.text?.secondary ?? customTheme.Gray ?? '',
+        customTheme.background?.primary ?? customTheme.Background ?? '',
+        0.5,
+      ),
     GradientColors: customTheme.ui?.gradient ?? customTheme.GradientColors,
   };
 
@@ -429,6 +442,7 @@ export function createCustomTheme(customTheme: CustomTheme): Theme {
     ui: {
       comment: customTheme.ui?.comment ?? colors.Comment,
       symbol: customTheme.ui?.symbol ?? colors.Gray,
+      dark: colors.DarkGray,
       gradient: customTheme.ui?.gradient ?? colors.GradientColors,
     },
     status: {
diff --git a/packages/cli/src/ui/themes/xcode.ts b/packages/cli/src/ui/themes/xcode.ts
index 690d238638..5d20f35c36 100644
--- a/packages/cli/src/ui/themes/xcode.ts
+++ b/packages/cli/src/ui/themes/xcode.ts
@@ -5,6 +5,7 @@
  */
 
 import { type ColorsTheme, Theme } from './theme.js';
+import { interpolateColor } from './color-utils.js';
 
 const xcodeColors: ColorsTheme = {
   type: 'light',
@@ -21,6 +22,7 @@ const xcodeColors: ColorsTheme = {
   DiffRemoved: '#FEDEDE',
   Comment: '#007400',
   Gray: '#c0c0c0',
+  DarkGray: interpolateColor('#c0c0c0', '#fff', 0.5),
   GradientColors: ['#1c00cf', '#007400'],
 };