Examine source code of Rainbow

{
  "name": "Tęcza",
  "manifest_version": 2,
  "version": "2.0",
  "theme": {
    "images": {
      "theme_frame": "1000004403.png"
    },
    "colors": {
      "frame": "rgba(207, 171, 255, 1)",
      "tab_background_text": "rgba(255, 255, 255, 1)",
      "toolbar": "rgba(0, 0, 0, 1)",
      "bookmark_text": "rgba(255, 255, 255, 1)",
      "toolbar_field": "rgba(120, 120, 120, 1)",
      "toolbar_field_text": "rgba(255, 255, 255, 1)",
      "tab_line": "rgba(115, 0, 255, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{89f501d7-9266-48d4-81d5-8d9e1c4e2e3d}"
    }
  }
}