diff --git a/apps/readest-app/src/__tests__/components/HighlightColorsEditor.test.tsx b/apps/readest-app/src/__tests__/components/HighlightColorsEditor.test.tsx
new file mode 100644
index 00000000..c6546b4e
--- /dev/null
+++ b/apps/readest-app/src/__tests__/components/HighlightColorsEditor.test.tsx
@@ -0,0 +1,115 @@
+import React, { useState } from 'react';
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { render, screen, cleanup, fireEvent } from '@testing-library/react';
+
+import HighlightColorsEditor from '@/components/settings/color/HighlightColorsEditor';
+import { HIGHLIGHT_COLOR_HEX } from '@/services/constants';
+import type { DefaultHighlightColor, HighlightColor, UserHighlightColor } from '@/types/book';
+
+vi.mock('@/hooks/useTranslation', () => ({
+  useTranslation: () => (s: string) => s,
+}));
+
+// Mocked SketchPicker that tracks mount/unmount via a shared module-level
+// registry, so we can detect whether the picker was remounted across a hex
+// change. Each mount gets a unique id; a mount is "alive" while its cleanup
+// hasn't run.
+const mountLog: Array<{ id: number; alive: boolean }> = [];
+let nextMountId = 0;
+
+vi.mock('react-color', () => ({
+  SketchPicker: ({
+    color,
+    onChange,
+  }: {
+    color: string;
+    onChange: (c: { hex: string }) => void;
+  }) => {
+    const [mountId] = useState(() => {
+      const id = nextMountId++;
+      mountLog.push({ id, alive: true });
+      return id;
+    });
+    React.useEffect(() => {
+      return () => {
+        const entry = mountLog.find((m) => m.id === mountId);
+        if (entry) entry.alive = false;
+      };
+    }, [mountId]);
+    return (
+      <div
+        data-testid='mock-sketch-picker'
+        data-mount-id={mountId}
+        data-color={color}
+        // Expose a way to trigger onChange as if from a drag.
+        onClick={() => onChange({ hex: '#112233' })}
+      />
+    );
+  },
+  ColorResult: undefined,
+}));
+
+afterEach(() => {
+  cleanup();
+  mountLog.length = 0;
+  nextMountId = 0;
+});
+
+const Harness: React.FC<{ initialUserColors: UserHighlightColor[] }> = ({ initialUserColors }) => {
+  const [userColors, setUserColors] = useState<UserHighlightColor[]>(initialUserColors);
+  const [customColors, setCustomColors] =
+    useState<Record<HighlightColor, string>>(HIGHLIGHT_COLOR_HEX);
+  const [labels, setLabels] = useState<Partial<Record<DefaultHighlightColor, string>>>({});
+
+  return (
+    <HighlightColorsEditor
+      customHighlightColors={customColors}
+      userHighlightColors={userColors}
+      defaultHighlightLabels={labels}
+      highlightOpacity={0.3}
+      isEink={false}
+      onCustomHighlightColorsChange={setCustomColors}
+      onUserHighlightColorsChange={setUserColors}
+      onDefaultHighlightLabelsChange={setLabels}
+      onOpacityChange={() => {}}
+    />
+  );
+};
+
+describe('HighlightColorsEditor — user color SketchPicker stability', () => {
+  it('keeps the SketchPicker mounted when the user-color hex updates (so drag is not interrupted)', () => {
+    render(<Harness initialUserColors={[{ hex: '#aabbcc' }]} />);
+
+    // The user color row's ColorInput renders a text input with the hex.
+    // Find it (the predefined palette also renders inputs; the user row's
+    // input is last in the document because it's rendered after the defaults).
+    const hexInputs = screen.getAllByDisplayValue(/^#/);
+    const userHexInput = hexInputs[hexInputs.length - 1]!;
+    expect(userHexInput).toHaveProperty('value', '#aabbcc');
+
+    // Open the SketchPicker for this user color.
+    fireEvent.click(userHexInput);
+
+    const picker = screen.getByTestId('mock-sketch-picker');
+    const initialMountId = picker.getAttribute('data-mount-id');
+    expect(initialMountId).not.toBeNull();
+
+    // Simulate an onChange coming from the SketchPicker during drag.
+    // (In the real picker this fires continuously as the user drags.)
+    fireEvent.click(picker);
+
+    // After the hex update, the picker should STILL be mounted (same id).
+    // If the parent row unmounted due to `key={hex}` changing, the original
+    // mount would be gone and React would have mounted a fresh one — the
+    // drag's window-level mouse listeners would be torn down with it.
+    const sameMount = mountLog.find((m) => String(m.id) === initialMountId);
+    expect(sameMount, 'SketchPicker mount with initial id should still exist').toBeDefined();
+    expect(sameMount!.alive, 'SketchPicker should not be unmounted on hex change').toBe(true);
+
+    // And a picker for the new color should still be visible in the DOM.
+    const pickerAfter = screen.queryByTestId('mock-sketch-picker');
+    expect(pickerAfter).not.toBeNull();
+    expect(pickerAfter!.getAttribute('data-color')).toBe('#112233');
+    expect(pickerAfter!.getAttribute('data-mount-id')).toBe(initialMountId);
+  });
+});
diff --git a/apps/readest-app/src/components/settings/color/HighlightColorsEditor.tsx b/apps/readest-app/src/components/settings/color/HighlightColorsEditor.tsx
index a2bfb287..837417e7 100644
--- a/apps/readest-app/src/components/settings/color/HighlightColorsEditor.tsx
+++ b/apps/readest-app/src/components/settings/color/HighlightColorsEditor.tsx
@@ -253,7 +253,7 @@ const HighlightColorsEditor: React.FC<HighlightColorsEditorProps> = ({
           {userHighlightColors.length > 0 && (
             <div className='grid grid-cols-3 gap-3 sm:grid-cols-5'>
               {userHighlightColors.map(({ hex, label }, index) => (
-                <div key={hex} className='group relative flex flex-col items-center gap-2'>
+                <div key={index} className='group relative flex flex-col items-center gap-2'>
                   <ColorCircle
                     hex={hex}
                     label={label ?? ''}