HTMLColor constructor
Implementation
HTMLColor(this.red, this.green, this.blue, [this.alpha]) {
_checkInRange('red', red, 0, 255);
_checkInRange('green', green, 0, 255);
_checkInRange('blue', blue, 0, 255);
if (alpha != null) {
_checkInRange('alpha', alpha!, 0, 1);
}
}