indigo top-level property Null safety

Implementation

NBColor indigo = const NBColor(
    0xff6366f1,
    <String, Color>{
      'indigo.50 ': Color(0xffeef2ff),
      'indigo.100': Color(0xffe0e7ff),
      'indigo.200': Color(0xffc7d2fe),
      'indigo.300': Color(0xffa5b4fc),
      'indigo.400': Color(0xff818cf8),
      'indigo.500': Color(0xff6366f1),
      'indigo.600': Color(0xff4f46e5),
      'indigo.700': Color(0xff4338ca),
      'indigo.800': Color(0xff3730a3),
      'indigo.900': Color(0xff312e81),
    },
    'indigo');