fillColor property
final
The fill color for selected toggle buttons.
If this property is null, then ToggleButtonTheme.of(context).fillColor is used. If ToggleButtonsThemeData.fillColor is also null, then the fill color is null.
If fillColor is a WidgetStateProperty<Color>, then WidgetStateProperty.resolve is used for the following WidgetStates:
Implementation
final Color? fillColor;