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Thanks @jajeanpierre for clarifying, I guess I was comparing it to humans and other animals. I've yet to experience any major health issues with chameleons luckily. Black tends to be necrosis in many creatures so I figured I'd mention that it could be something to worry about.
When I first got one of my Nosy Be girls (~6 months old) she had a little bit of black on her lip (see picture). I pointed it out to the breeder and they didn't think much of it. I took her in to a pet shop where they breed panthers and they suggested it was was cut and that I should rub a small drop (1/4 pea size) of gel Vetricyn on the area once/twice a day for a week. They said if that didn't work after a week I should take her over to the exotic animal vet in the area. I used the Vetricyn for ~4 days and the black went away. I then left on a work trip for 2 weeks while my roommates took care of the chams. When I got back the black was back and her lips were a little bit separated and looking worse so I took her to the vet. They swabbed out her mouth with a q-tip and there was a bunch of gross infection stuff in there. They gave me 30 days worth of antibiotic shots to give her (10 doses so once every 3 days) and they did a culture. Turns out it was a bacterial infection of 3 different types of bacteria causing mouth rot. She's all better now, and I think if I had been home still using the Vetriycn I wouldn't have needed to go to the vet (and I would have avoided the $330 bill) but because of the 2 weeks with less health monitoring she got worse.
That's just my experience with a little black on the lip. I can't say if that is your panthers problem or not but I can share my experience. Definitely monitor him to see if it gets worse and if his lips start separating/opening slightly it's probably an infection and you should take him to a vet (if you have one in your area that has dealt with chameleons.