function setNormalizedColorAlpha(input: number, alpha: number): number {
  if (alpha < 0) {
    alpha = 0;
  } else if (alpha > 1) {
    alpha = 1;
  }

  alpha = Math.round(alpha * 255);
  // magic bitshift guarantees we return an unsigned int
  return ((input & 0xffffff00) | alpha) >>> 0;
}
number should be a color processed by `normalizeColor`
alpha should be number between 0 and 1