I never thought about this before. I don't know if my lips are dark or not, but they are large. I used to play the trumpet, and they were super huge then. I get a lot of compliments from guys about my lips. If you like guys, your prominent lips might be a bonus if you could get used to them.
I chew on my lips a lot too, and I feel you on the staining issue. Even if you don't bite enough to scab, the loose skin seems to pick up coffee and whatnot. I dunno.
A trick I was taught that is supposed to help with acne or rosacea or other reddening stuff on facial skin was putting allergy eyedrops on inflamed patches. That might could help with your lips, but it seems like such different types of skin that it might be useless.
Good luck.