Examine source code of Background-Rainbow

{
  "name": "Background-Rainbow",
  "manifest_version": 2,
  "version": "3.0",
  "theme": {
    "images": {
      "theme_frame": "3c074a911d21959311672c676c226812.jpg"
    },
    "colors": {
      "frame": "rgba(145, 0, 255, 1)",
      "tab_background_text": "rgba(145, 0, 255, 1)",
      "bookmark_text": "rgba(145, 0, 255, 1)",
      "toolbar_field_text": "rgba(145, 0, 255, 1)"
    }
  }
}