Dart APIunself_componentUnselfNavigationBarBackButtoncolor color property Null safety Color? color final Implementation final Color? color; unself_component unself_component UnselfNavigationBarBackButton color property UnselfNavigationBarBackButton class Constructors UnselfNavigationBarBackButton Properties color hashCode key onPressed previousPageTitle runtimeType Methods build createElement debugDescribeChildren debugFillProperties noSuchMethod toDiagnosticsNode toString toStringDeep toStringShallow toStringShort Operators operator ==