blend method
Implementation
Color blend(Color other, double fractionOther) {
var fractionThis = 1.0 - fractionOther;
return Color(
(r * fractionThis + other.r * fractionOther).toInt(),
(g * fractionThis + other.g * fractionOther).toInt(),
(b * fractionThis + other.b * fractionOther).toInt());
}