Examine source code of Simple Theme 2

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#545252",
      "tab_background_text": "#545252"
    }
  },
  "version": "2.0",
  "name": "Simple Theme 2",
  "manifest_version": 2,
  "description": "This is a theme if you want your browser to look clean."
}