Examine source code of Hydrangea...

{
  "name": "Hydrangea...",
  "manifest_version": 2,
  "version": "3.0",
  "theme": {
    "images": {
      "theme_frame": "HydrangiaH.jpg"
    },
    "colors": {
      "frame": "rgba(56, 118, 194, 1)",
      "tab_background_text": "rgba(255, 255, 255, 1)",
      "toolbar": "rgba(57, 115, 196, 0)",
      "bookmark_text": "rgba(255, 255, 255, 1)",
      "toolbar_field": "rgba(57, 115, 196, 0.06)",
      "toolbar_field_text": "rgba(255, 255, 255, 1)",
      "tab_line": "rgba(255, 255, 255, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d04958fd-ffac-4100-b5f5-94214b0ade9e}"
    }
  }
}