Feature Request: Support for custom color themes

[PolyphonyRequiem]

Feature Request: Custom Color Themes

Problem

Currently, the /theme command only supports auto, dark, and light color modes. There is no way to customize the color palette used by the CLI (e.g., accent colors, background tints, text colors, etc.).

Use Case

When running multiple Copilot CLI sessions with different configurations (e.g., a standard session vs. an admin session with a different model), it would be very helpful to visually distinguish them with distinct color themes. Right now, the only option is to change the terminal emulator's color scheme, which is a workaround rather than a first-class solution.

Proposed Solution

Support custom themes via configuration, for example in ~/.copilot/config.json or a dedicated ~/.copilot/themes/ directory. A theme could define colors for:

• Background/foreground
• Accent colors (prompt, highlights, borders)
• Status bar / footer colors
• Diff colors
• Agent output colors

Example config:

{
  "theme": "admin",
  "themes": {
    "admin": {
      "accent": "#7C4DFF",
      "background": "#1A0A2E",
      "foreground": "#E0D0FF"
    }
  }
}

This would also allow users to share themes, which could build community engagement.

Alternatives Considered

• Using Windows Terminal / iTerm2 color schemes as a workaround (current approach)
• Using /theme dark vs /theme light to differentiate sessions (limited)

Additional Context

Running on Windows with multiple desktop shortcuts for different Copilot configurations (different models, admin vs. non-admin). Visual distinction at the Copilot level would be much cleaner than relying on terminal emulator theming.