Examine source code of ColoCircles

{
  "theme": {
    "images": {
      "theme_frame": "circlehead.jpg"
    },
    "colors": {
      "frame": "#8a8686",
      "tab_background_text": "#0b0bb5"
    }
  },
  "version": "2.0",
  "name": "ColoCircles",
  "manifest_version": 2,
  "description": "Color circles like bubbles floating around"
}