[FEATURE] Customizable background color for permission/question prompts

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

When Claude Code stops to ask for permission (tool approval) or asks a question (AskUserQuestion), the prompt lines look visually similar to the rest of the terminal output. To know that Claude is waiting for input, you have to consciously read the text — there's no instant visual signal.

This is the same problem as "is Claude still working?" but for the opposite state: "has Claude stopped and needs me?" If you're glancing at the terminal while multitasking, both states look similar.

Proposed Solution

Allow users to set a background color (or other ANSI styling) on lines where Claude is waiting for user input — permission prompts, AskUserQuestion dialogs, etc. For example:

{
  "promptStyle": {
    "backgroundColor": "yellow"
  }
}

Or more flexibly with raw ANSI:

{
  "promptStyle": {
    "style": "\^[[43m"
  }
}

A subtle colored background on the prompt line would make the "needs your attention" state instantly recognizable at a glance without needing to read text.

Alternative Solutions

• #13024 requests a hook for when Claude is waiting for input (to trigger a chime or notification). That solves the "not looking at terminal" case but doesn't help when you're glancing at the screen.
• #25307 (closed) requested distinct tab title indicators for waiting-for-input vs done. That helps when the terminal is in another tab, but not when the terminal is visible on screen.
• #21663 requests syntax highlighting for dangerous commands in prompts. That's about the content of permission prompts, while this request is about the visual state of any prompt.
• A general theming system would also cover this, but a single background color setting for prompt lines would be much simpler to implement and covers the core use case.

Priority

Medium - Nice to have improvement

Feature Category

Configuration and settings

Additional Context

Companion to #29473 which requests the same treatment for the activity indicator line. Together they would give users instant at-a-glance awareness of Claude's state: colored background = something is happening (either working or waiting for input), no colored background = idle/done.