Yes, why is it that some men have darker penises? I friend told me that his penis was darker than the rest of his skin. I took his word for it. Why would he lie? Too modest to to undress, but there you are. Some people are like that, and it must be respected. I wonder if there is a separate gene for skin pigmentation of the penis. No doubt the media would have a field day with some published academic paper on the topic. Just be hoped that such people will never need a skin graft in that area.