Examine source code of uicolors

{
  "name": "uicolors",
  "manifest_version": 2,
  "version": "2.0",
  "theme": {
    "images": {
      "theme_frame": "Empty.png"
    },
    "colors": {
      "frame": "rgba(23, 23, 23, 1)",
      "tab_background_text": "rgba(200, 200, 200, 1)",
      "toolbar": "rgba(0, 0, 0, 0)",
      "bookmark_text": "rgba(200, 200, 200, 1)",
      "toolbar_field": "rgba(0, 0, 0, 0)",
      "toolbar_field_text": "rgba(200, 200, 200, 1)",
      "tab_line": "rgba(0, 0, 0, 0)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{63bf94b1-4297-4135-9133-59d970d206ad}"
    }
  }
}