whiten method
Implementation
Color whiten(double amount) {
assert(amount >= 0 && amount <= 1);
double r = clampDouble(this.r * amount, 0.0, 1.0);
double g = clampDouble(this.g * amount, 0.0, 1.0);
double b = clampDouble(this.b * amount, 0.0, 1.0);
return Color.from(red:r, green:g, blue:b, alpha: a);
}