chromium/chrome/test/data/extensions/theme_grey_ntp_white_logo/manifest.json

{
   "manifest_version": 2,
   "name": "minimal",
   "theme": {
      "colors": {
         "ntp_background": [100, 100, 100]
      },
      "properties": {
         "ntp_logo_alternate": 1
      }

   },
   "version": "2.0"
}