Examine source code of Simple Indigo

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Simple Purple",
  "theme": {
    "images": {},
    "properties": {},
    "colors": {
      "toolbar": "rgb(20, 22, 51)",
      "toolbar_text": "rgb(185, 189, 255)",
      "frame": "rgb(32, 34, 67)",
      "tab_background_text": "rgb(185, 189, 255)",
      "toolbar_field": "rgb(32, 34, 67)",
      "toolbar_field_text": "rgb(185, 189, 255)",
      "tab_line": "rgba(20, 22, 51, 0.01)",
      "popup": "rgb(32, 34, 67)",
      "popup_text": "rgb(185, 189, 255)",
      "tab_loading": "rgba(20, 22, 51, 0.01)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d7ab7273-e13a-481e-97c0-9a9b0fad3330}"
    }
  }
}