Examine source code of Medium Grey

{
  "theme": {
    "images": {
      "theme_frame": "DarkGrayHeader.jpg"
    },
    "colors": {
      "frame": "#ffffff",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Medium Grey",
  "manifest_version": 2,
  "description": "Just a solid medium grey color [rgb:150], with light text"
}