mix method
Implementation
ColorValue mix(String value, double amount) {
final other = maybeParse(value)!;
final newa = ((other.a - a) * amount + a).round();
final newr = ((other.r - r) * amount + r).round();
final newg = ((other.g - g) * amount + g).round();
final newb = ((other.b - b) * amount + b).round();
return ColorValue._(newr, newg, newb, newa);
}