fillColor property Null safety

MaterialStateProperty<Color?>? fillColor
final

The color that fills the checkbox, in all MaterialStates.

Resolves in the following states:

link
This example resolves the fillColor based on the current MaterialState of the Checkbox, providing a different Color when it is MaterialState.disabled. 
Checkbox(
  value: true,
  onChanged: (_){},
  fillColor: MaterialStateProperty.resolveWith<Color>((Set<MaterialState> states) {
    if (states.contains(MaterialState.disabled)) {
      return Colors.orange.withOpacity(.32);
    }
    return Colors.orange;
  })
)

If specified, overrides the default value of Checkbox.fillColor.

Implementation

final MaterialStateProperty<Color?>? fillColor;