The color to use when the BuildContext implies a combination of dark mode, normal contrast, and base interface elevation.
- has a CupertinoTheme whose CupertinoThemeData.brightness is Brightness.dark, or a MediaQuery whose MediaQueryData.platformBrightness is Brightness.dark.
- has a MediaQuery whose MediaQueryData.highContrast is
- has a CupertinoUserInterfaceLevel that indicates CupertinoUserInterfaceLevelData.base.
final Color darkColor