Talk:Ken Kaneki/@comment-26041360-20150323222530/@comment-10733658-20150323231143

Difficult to say, but there are things that can cause darkening of the lips in real life. You can get dark blue from anemia, cyanosis (deoxygenated blood), cancers, or poisoning.

If I had to guess, it could be from repeated regeneration from chewing on them. (Like, I think the white hair + darkened body parts is likely a result of Ghoul regeneration going wonky since those things happen in real in relation to immune reactions but are much slower.)