NSFW -- Is there a word for the darkened area around a person's anus?

Some people don’t have such an area. But most humans do. I know good and well it isn’t staining from the diet. It’s a difference in basic skin color, and it’s often also seen around the labial lips and on the male scrotum. Some theorize it’s a genetic adaptation that enhances mating. These people theorize that it’s caused by thinner than usual skin, putting nerve endings nearer the surface, and thus making those who have this adaptation better choices as mates. Others find it offensive, and actually seek quackticioners who will bleach the skin using dangerously powerful, burning chemicals to normalize the nether region skin tone for them.

First, do you think it’s disgusting or sexy? And second, whatever your take on the attractiveness, what is it called?