验证十六进制颜色值 (#RGB, #RGBA, #RRGGBB, #RRGGBBAA)
bool isHexColor(String? color) { const pattern = r'^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3}|[A-Fa-f0-9]{8}|[A-Fa-f0-9]{4})$'; return hasMatch(color, pattern); }