Examine source code of colour_mode

{
  "manifest_version": 2,
  "name": "inShorts in dark",
  "version": "2.0.2resigned1",
  "homepage_url": "https://github.com/viswanathamsantosh/inshorts",
  "description": "Read your favourite news on inShorts by dimming the light right away on your browser.",
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "browser_action": {
    "browser_style": true,
    "default_icon": {
      "19": "icons/icon-19.png",
      "38": "icons/icon-38.png"
    },
    "default_title": "Turn on or off"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{6084fc85-9b69-4af5-bf99-193a86d5701f}"
    }
  }
}