function isColorAlphaDirty(currentColor, previousColor) {
  if (!defined(currentColor) && !defined(previousColor)) {
    return false;
  }

  if (defined(currentColor) !== defined(previousColor)) {
    return true;
  }

  const currentAlpha = currentColor.alpha;
  const previousAlpha = previousColor.alpha;
  return (
    Math.floor(currentAlpha) !== Math.floor(previousAlpha) ||
    Math.ceil(currentAlpha) !== Math.ceil(previousAlpha)
  );
}
Returns whether the alpha state has changed between invisible,
 translucent, or opaque.

 @private