Sometimes, it's genetics and if it's that, then your solution is permanent tint at a clinic or something.
If it's not genetics, then I suggest you try what I did 😊 (my lips used to be really dark because when I was kid, I used expired lipstick 😂) it's not as dark as it used to be, I could say it is better and lighter now. So what I'm practicing now, after I brush my teeth, I used my toothbrush to lightly brush on my lips too (gently and rinse the toothpaste off first! 😂). I don't wear lipstick (traumatized 😅), I only use liptints and I never forget to apply vaseline or lip balm. If you want to, there are also balms that has spf on it, that could be helpful to you too. 😊