surfaceTintColor property
final
The color used as an overlay on backgroundColor to indicate elevation.
If null, MaterialBannerThemeData.surfaceTintColor is used. If that is also null, the default value is Colors.transparent.
This is not recommended for use. Material 3 spec introduced a set of tone-based surfaces and surface containers in its ColorScheme, which provide more flexibility. The intention is to eventually remove surface tint color from the framework.
Implementation
final Color? surfaceTintColor;