colorScheme property
A set of thirteen colors that can be used to derive the badge theme's colors.
This property was added much later than the theme's set of highly specific colors, like ThemeData.badgeColor, ThemeData.highlightColor, ThemeData.splashColor etc.
The colors for new badge classes can be defined exclusively in terms of colorScheme. When it's possible, the existing badges will (continue to) gradually migrate to it.
Implementation
final ColorScheme? colorScheme;