hcToHex method
return hex String
Implementation
String hcToHex({bool leadingHashSign = true, bool includeAlpha = false}) =>
'${leadingHashSign ? '#' : ''}'
'${includeAlpha ? alpha.toRadixString(16).padLeft(2, '0') : ''}'
'${red.toRadixString(16).padLeft(2, '0')}'
'${green.toRadixString(16).padLeft(2, '0')}'
'${blue.toRadixString(16).padLeft(2, '0')}';