Color.fromRGBO(153, 50, 204, 0.5)
// opacity:  透明度 0～1

Color.fromARGB(255, 55, 1, 200)
// a:  alpha值，0是透明的，255是完全不透明的

Color(0xFFb74093)
Color(0xffb74093)

Colors.blue

class HexColor extends Color {
  static int _getColorFromHex(String hexColor) {
    hexColor = hexColor.toUpperCase().replaceAll("#", "");
    if (hexColor.length == 6) {
      hexColor = "FF" + hexColor;
    }
    return int.parse(hexColor, radix: 16);
  }

  HexColor(final String hexColor) : super(_getColorFromHex(hexColor));
}

HexColor("#b74093")

const Opacity({
  Key key,
  @required this.opacity, // 透明度opacity >= 0.0 && opacity <= 1.0
  this.alwaysIncludeSemantics = false,
  Widget child,
})