I think you'd be surprised at how light and subtle these things can be. I remember seeing some on something printed back in early 2000s and they were yellow dots barely registerable under a magnifying loupe, never mind by eye up close.
Which, if the same sort of case here, makes the CCD(s) on the phone here particularly impressive.
Which, if the same sort of case here, makes the CCD(s) on the phone here particularly impressive.