Examine source code of Material Rainbow

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#3d3d3d",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Material Rainbow",
  "manifest_version": 2,
  "description": "A simple, elegant gradient featuring material blue, pink and orange colors."
}