Feature Request: Fine-grained per-element theming (border colors, chevron, prompt vs response foreground)

[harshit7962]

Describe the feature or problem you'd like to solve

The /theme command currently supports three high-level modes (auto, dark, light) that control overall ANSI color contrast — which is great for a baseline. It would be wonderful to take this further with fine-grained theming that allows customizing the appearance of individual UI elements. This would help users visually distinguish between user prompts, assistant responses, status indicators, and tool output — especially during long sessions where scrolling back to find specific parts of the conversation can be challenging.

Proposed solution

It would be great to support per-element styling overrides in config.json (or a dedicated theme.json file). We can think along the lines of:

UI Element	Customization
User prompt text	Foreground color
Assistant response text	Foreground color
User chevron/icon (❯)	Color, optionally the character itself
Prompt input border / frame	Border color, style
"Thinking" / status indicators	Foreground color, animation style
Tool execution output	Foreground color (muted vs. primary)
Diff view	Addition/deletion colors
Code blocks	Background and foreground colors
Timeline / progress bars	Accent color

A possible config.json structure could look like:

{
  "theme": "dark",
  "themeOverrides": {
    "userPromptFg": "green",
    "assistantResponseFg": "white",
    "userChevronColor": "cyan",
    "promptBorderColor": "blue",
    "thinkingIndicatorFg": "yellow",
    "toolOutputFg": "gray",
    "diffAddFg": "#22c55e",
    "diffRemoveFg": "#ef4444",
    "codeBlockBg": "#1e1e2e"
  }
}

Supporting both named ANSI colors ("green", "cyan") and hex values ("#00FF00") for true-color terminals would make this flexible for a wide range of setups.

Example prompts or workflows

1. Users who want their prompts to stand out could set userPromptFg: "green" and promptBorderColor: "cyan" while keeping responses in default white — making it easy to scroll back and locate what was typed.
2. Streamers could create visually appealing themes with branded accent colors.
3. Users with accessibility needs could increase contrast on specific elements without changing the entire terminal color scheme.
4. Teams could create and share theme JSON files for a consistent experience.

Additional context

• Environment: Windows, Windows Terminal, Copilot CLI latest

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