The color to use for the modal barrier. If this is null, the barrier will be transparent.
The modal barrier is the scrim that is rendered behind each route, which generally prevents the user from interacting with the route below the current route, and normally partially obscures such routes.
For example, when a dialog is on the screen, the page below the dialog is usually darkened by the modal barrier.
The color is ignored, and the barrier made invisible, when ModalRoute.offstage is true.
While the route is animating into position, the color is animated from transparent to the specified color.
It is safe to use
navigator.context to look up inherited
widgets here, because the Navigator calls
changedExternalState whenever its dependencies change, and
changedExternalState causes the modal barrier to rebuild.
Color get barrierColor => Theme.of(navigator.context).colorScheme.background;
@override Color? get barrierColor => null;