iterm2: Supporting dark-light pairs

[JamyGolden]

This issue existed before moving to tinted-terminal: tinted-theming/tinted-iterm2#9

[seidtgeist]

iterm2-auto-theme-switch.mov

FYI, i finally made this work by generating a iTerm2 Dynamic Profile at ~/Library/Application\ Support/iTerm2/DynamicProfiles/<profile_name>.json:

(Warning: Remove the comments from the final file! I just put them here for illustrative purposes.)

{
  // Any properties as per the documentation, but these are required:
  "name": "<profile_name>",
  "guid": "<some guid>",

 // Enable automatic light/dark mode switching
 "Use Separate Colors for Light and Dark Mode": true,

  // Color properties need three variants each:
  // 1. Base variant (no suffix) - should match whatever variant
  // 2. Light variant - used in light mode
  // 3. Dark variant - used in dark mode

  // Example with Background Color:
  "Background Color": {
    "Red Component": 0.98,
    "Green Component": 0.98,
    "Blue Component": 0.98
  },
  "Background Color (Light)": {
    "Red Component": 0.98,
    "Green Component": 0.98,
    "Blue Component": 0.98
  },
  "Background Color (Dark)": {
    "Red Component": 0.0,
    "Green Component": 0.0,
    "Blue Component": 0.0
  },

  // Same pattern for all color properties:
  "Foreground Color": { /* base values */ },
  "Foreground Color (Light)": { /* light values */ },
  "Foreground Color (Dark)": { /* dark values */ },

  // ANSI colors (0-15) follow the same pattern:
  "Ansi 0 Color": { /* base values */ },
  "Ansi 0 Color (Light)": { /* light values */ },
  "Ansi 0 Color (Dark)": { /* dark values */ },
  // ... through Ansi 15 Color

  // Other color properties that support variants:
  // Bold Color, Cursor Color, Cursor Text Color, Selection Color,
  // Selected Text Color, Link Color, Badge Color, etc.
}

The key insight is that iTerm2 will automatically switch between the (Light) and (Dark) variants based on the macOS system appearance. This allows a single profile to seamlessly support both light and dark themes without any manual switching or external scripts.

For tinted-theming, this means you could generate a single iTerm2 profile that includes both a light and dark base16/base24 theme, and iTerm2 will handle the switching automatically!

In my particular case, my nix-darwin & home-manager setup is reading YAML files from tinty's schemes package (or rather its nixpkg version) and creating a managed ~/Library/Application\ Support/iTerm2/DynamicProfiles/tmux.json file which iTerm will use for my tmux sessions.

What's really neat is that programs with base16 themes, such as helix (e.g. base16_terminal), will just inherit the iTerm2 colors, so they'll change at runtime accordingly.

Edit: Added some more details to here: nix-community/stylix#1774