Examine source code of Rainbow gradient

{
  "theme": {
    "images": {
      "theme_frame": "firefoxheadergradient5.jpg"
    },
    "colors": {
      "frame": "#756a6a",
      "tab_background_text": "#0a0a0a"
    }
  },
  "version": "2.0",
  "name": "Rainbow gradient",
  "manifest_version": 2,
  "description": "an aurora of colour through the spectrum"
}