Continuity mistake: Dr. Cox's hair colour and length change back and forth significantly during the episode.
Continuity mistake: S6-E01. When Perry is lecturing the interns, the sweat stains on his shirt change between shots. For example, when we first see him there is no sweat around the collar, but in close-ups there is sweat around the collar.
Continuity mistake: In series 6, episode 1 ('My Mirror Image'), the length of Dr Cox's hair fluctuates noticeably between scenes.
Continuity mistake: When JD gets hit by the blue paint and confetti by the Blue Man Group at their concert, most confetti in the next scene disappears and JD is almost covered only by paint.
Answer: No, it was a fake, they used a stamp.
It is real.