colorToHex function
Formats c as a #RRGGBB hex string, or empty if null.
Implementation
String colorToHex(UvRgb? c) {
if (c == null) return '';
final r = c.r.clamp(0, 255);
final g = c.g.clamp(0, 255);
final b = c.b.clamp(0, 255);
return '#${r.toRadixString(16).padLeft(2, '0')}'
'${g.toRadixString(16).padLeft(2, '0')}'
'${b.toRadixString(16).padLeft(2, '0')}';
}