add method
Implementation
Color add(Color other, [double? fractionOther]) {
fractionOther ??= 1.0;
return Color(
(r + other.r * fractionOther).clamp(0, 255).toInt(),
(g + other.g * fractionOther).clamp(0, 255).toInt(),
(b + other.b * fractionOther).clamp(0, 255).toInt());
}