Examine source code of George peabody library,

{
  "name": "Rainbow cloud",
  "manifest_version": 2,
  "version": "2.0",
  "theme": {
    "images": {
      "theme_frame": "George peabody library.jpg"
    },
    "colors": {
      "frame": "rgba(229, 230, 232, 1)",
      "tab_background_text": "rgba(0, 0, 0, 1)",
      "toolbar": "rgba(191, 57, 57, 1)",
      "toolbar_field": "rgba(207, 83, 83, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{fa4a97df-9fdf-45ca-ae88-c479b2dde0d5}"
    }
  }
}