newColor top-level property Null safety

Implementation

NBColor newColor = const NBColor(
    0xff737373,
    <String, Color>{
      'newColor.400': Color(0xffa3a3a3),
      'newColor.500': Color(0xff737373),
      'newColor.600': Color(0xff525252),
      'newColor.700': Color(0xff404040),
      'newColor.1000': Color(0xff404040),
    },
    'newColor');