overlayColor property Null safety
Defines the ink response focus, hover, and splash colors.
This default null property can be used as an alternative to focusColor, hoverColor, highlightColor, and splashColor. If non-null, it is resolved against one of MaterialState.focused, MaterialState.hovered, and MaterialState.pressed. It's convenient to use when the parent widget can pass along its own MaterialStateProperty value for the overlay color.
MaterialState.pressed triggers a ripple (an ink splash), per the current Material Design spec. The overlayColor doesn't map a state to highlightColor because a separate highlight is not used by the current design guidelines. See https://material.io/design/interaction/states.html#pressed
- The Material Design specification for overlay colors and how they match a component's state: material.io/design/interaction/states.html#anatomy.
final MaterialStateProperty<Color?>? overlayColor;