How old is your dog? When Clipper was 12 years old, I noticed his lips drooping on one side, I posted asking about drooping lip. The vet had said it looked infected and put him on clindamycin, it cleared up, he also had said it could be a autoimmune thing too. If it looks different from the other side you might want to have the vet take a look.
How long has this been going on? If it’s something new I would think more of it. Otherwise I still think it looks okay. Are you more worried about the drooping or the color? Because my dog’s lips droop just like that.
If you’re worried, go to the vet. That’s always the best choice for questions you have.