toHex method
Returns this color encoded as an uppercase hexadecimal RGBA string.
Format: RRGGBBAA
Example:
color.toHex(); // "FF0000FF"
Implementation
String toHex() =>
'${r.toRadixString(16).padLeft(2, '0').toUpperCase()}'
'${g.toRadixString(16).padLeft(2, '0').toUpperCase()}'
'${b.toRadixString(16).padLeft(2, '0').toUpperCase()}'
'${a.toRadixString(16).padLeft(2, '0').toUpperCase()}';