UIColorName
The name of a color to use as the background color on the launch screen.
Discussion
Provide a value for this key that’s the name of a color in your asset catalog. You use the same string for the value that you might use when calling the init(named:) initializer of UIColor.
If you don’t set a color, the system uses a default of systemBackground, which varies according to whether the user has selected the light appearance or Dark Mode for the device.