Overview
When your web app is loading from a user's homescreen, the browser uses the
background_color property to draw the background color of the browser while
the app loads. This creates a smooth transition between launching the app and
loading the app's content.
Recommendations
Add a background_color property in your Web App Manifest. The value can be any
valid CSS color.
{
...
"background_color": "cornflowerblue",
...
}
Check out Manifest Exists for a list of guides that teach you how to properly implement and test "Add to Homescreen" support in your app.
More information
Audit passes if the manifest contains a background_color property.
The manifest that Lighthouse fetches is separate from the one that Chrome is
using on the page, which can possibly cause inaccurate results. Lighthouse does
not validate that the value is a valid CSS color.