People use lipliner to get the definiton that you dislike.
As you get older your lips will thin, lose their color and definition. Enjoy it while you have it.
Cheap lipsticks have cheap oils in them which interact with the sun and discolor your skin, the same ges for some cheap foundations too. So, be careful what products you are using. Get rid of dark edges/spots with Glycolic. Ask your Dermatlogist. Apply foundation all over your lips too and then outline lips with desired lip pencil, fill in with lipstick.