surfaceTintColor property Null safety
The color used as an overlay on color to indicate elevation.
If this is null, no overlay will be applied. Otherwise the color will be composited on top of color with an opacity related to elevation and used to paint the background of the BottomAppBar.
The default is null.
See Material.surfaceTintColor for more details on how this overlay is applied.
final Color? surfaceTintColor;