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

{
   "manifest_version": 2,
   "name": "minimal",
   "theme": {
      "colors": {
         "ntp_background": [150, 150, 100]
      },
      "images": {
         "theme_ntp_background": "background.jpg"
      }

   },
   "version": "2.0"
}