While some of it might be the blood, the other part is that the skin around the genitals has more melanocytes than the skin in other areas. The reason your penis is darker than the rest of your body is the same reason that black people are darker than white people.
To some degree, this is not surprising: Humans did not start off wearing clothes. It is not surprising that humans have ways of fending off the sun around their genitals such as pubic hair as well as better tanning.
Rrhain
WWJD? JWRTFM!
™ Version 4.2
