Examine source code of Watercolor Purples....

{
  "name": "Watercolor Purples....",
  "manifest_version": 2,
  "version": "4.0",
  "theme": {
    "images": {
      "theme_frame": "WatercolorsPurplesH.jpg"
    },
    "colors": {
      "frame": "rgba(115, 56, 242, 1)",
      "tab_background_text": "rgba(255, 255, 255, 1)",
      "toolbar": "rgba(93, 11, 186, 0)",
      "bookmark_text": "rgba(255, 255, 255, 1)",
      "toolbar_field": "rgba(72, 9, 145, 0.05)",
      "toolbar_field_text": "rgba(255, 255, 255, 1)",
      "tab_line": "rgba(255, 255, 255, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d30b1841-3093-441a-9c05-0c8b95201907}"
    }
  }
}