[FEATURE] Configurable diff view background colors

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

The diff view in Claude Code shows hard-coded red/green background
highlights for removed/added lines. These backgrounds are visually
heavy and cannot be customized through any settings. On dark terminals,
the bright colored blocks make the code harder to read.

Proposed Solution

Add a setting in Claude Code's settings.json to control diff view style. For example:

"diffStyle": "minimal" — show only text color and +/- indicators, no background highlight
"diffStyle": "default" — keep current red/green background (default)

This would allow users to choose a less visually noisy diff display.

Alternative Solutions

I tried modifying the Windows Terminal color scheme (red/green colors)
to make the diff backgrounds darker, but Claude Code uses true-color
(24-bit RGB) escape codes that bypass the terminal's color scheme entirely.
There is currently no workaround available.

Priority

Low - Nice to have

Feature Category

Interactive mode (TUI)

Use Case Example

When Claude Code edits a file, the diff view shows bright red/green
background blocks that are visually distracting on dark terminals.
A minimal diff style with only colored text and +/- indicators
would make code changes much easier to read.

Additional Context

_No response_