What is it that makes lips change color?

I’m not sure if everyones lips are like this, so I’ll just speak for myself. I’ve been curious as to why this happens for as long as I can remember. Enter: Fluther!

My lips are always a different color. I never wear anything on them except chapstick, which is not colored, but sometimes they aren’t much darker than my skin and sometimes they’re bright red. I personally hate when they’re bright red. I look sickly and awful. Usually they are a medium pink, and then for no reason I’ll go look in the mirror randomly and they’re 10 shades paler.

I haven’t noticed any activities that have an impact on the color…except that after making out they’re always redder, but that’s explainable. So I simply don’t get it. Can anyone offer some insight?

:)