I've been smoking pot since the 9th grade (I'm 22 now) and I've never had a problem with my lips changing color. I think you could solve the problem by exfoliating your lips. Everytime you brush your teeth, GENTLY massage your lips with the toothbrush when it's all foamy with toothpaste. It also helps prevent chapping too. Also, try wearing a little chapstick before you smoke. It will coat your lips and may prevent resin from sticking to them. Hope this helps.