overlayColor property
final
Defines the ink response focus, hover, and splash colors.
If non-null, it is resolved against one of MaterialState.focused, MaterialState.hovered, and MaterialState.pressed.
MaterialState.pressed triggers a ripple (an ink splash), per the current Material Design spec.
If the overlay color is null or resolves to null, then the default values for InkResponse.focusColor, InkResponse.hoverColor, InkResponse.splashColor, and InkResponse.highlightColor will be used instead.
Implementation
final MaterialStateProperty<Color?>? overlayColor;