Without wearing any lip gloss put Vaseline or lip balm on your lips then brush them or you can use rose water so it. It’s basically exfoliates them leaving new skin which is pinker and looks better.
There is a great home remedy for dark lips. Crush some rose petals and mix them with honey. Apply this on your lips and keep overnight. If regularly done, it will give you pink lips.
Find out the cause of dark lips, can be due to poisoning, stains or genetics.
The solution is different for each.
For Genetics, the only solution is through cosmetics