I just got cut my 4 yr old son s hair cut only to discover a black patch under his scalp. I first thought it was from the clippers at the barber, oil, burn something but, it s not. It s been a week and it hasn t gone away, has not gotten bigger or anything. It doesn t hurt him when pressed, it s not raised and there is no patching or bald spots. I may also mention he s a redhead, hence extremly fair. What could this be?