Turn a HEX color into Flutter Color code, or the other way round. Includes opacity and CSS values.
Works with #6D4BC1, #RGB, #RRGGBBAA (CSS), 0xFF6D4BC1, Color(0xFF6D4BC1), rgb(109, 75, 193) and Color.fromARGB(...). A hex without # and with 8 digits is read as Flutter AARRGGBB.