[FEATURE] Feature Request: Theme color customization for diff highlighting

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Currently, Claude Code offers preset themes (Dark mode, ANSI only, etc.), but users cannot customize individual colors.

• I like the overall colors of the default Dark mode
• But the background colors for added/removed lines in diffs are too intense and strain my eyes
• So I switched to ANSI colors only theme, and I enjoy the cute features like loading indicators
• But it lacks background colors for added/removed lines in diffs, which is inconvenient
• The other dark theme (Dark mode - colorblind-friendly) has a color scheme that doesn't suit my preferences

Proposed Solution

Allow users to customize theme colors via ~/.claude/settings.json or a separate theme config file.

Alternative Solutions

{
"theme": {
"base": "ansi-only",
"overrides": {
"diffAddedBackground": "rgba(0, 255, 0, 0.1)",
"diffRemovedBackground": "rgba(255, 0, 0, 0.1)"
}
}
}

Priority

Low - Nice to have

Feature Category

Interactive mode (TUI)

Use Case Example

Users with different visual preferences or accessibility needs could adjust colors without switching entire themes.

Additional Context

The existence of tweakcc shows there's user demand for theme customization. A built-in solution would be more
stable and maintainable.