Examine source code of Greetings,

{
  "name": "Greetings,",
  "manifest_version": 2,
  "version": "1.0",
  "theme": {
    "images": {
      "theme_frame": "Hello!.png"
    },
    "colors": {
      "frame": "rgba(0, 81, 255, 1)",
      "tab_background_text": "rgba(0, 0, 0, 1)",
      "toolbar": "rgba(223, 255, 18, 1)",
      "bookmark_text": "rgba(225, 0, 255, 1)",
      "toolbar_field": "rgba(0, 221, 255, 1)",
      "toolbar_field_text": "rgba(0, 0, 0, 1)"
    }
  }
}