Now this was funny. Thank you.
No lips? Hmmm. I’m imagining a horror movie. Know what I mean? Ever use your middle and ring fingers to spread your lips apart, showing your teeth and gums? I’m thinking of the same thing, but without the fingers.
We have lips, like chimps, for manipulating food. Fruit, specifically. Have you ever seen a chimp take apart an orange or a banana?
I’d vote that our lips are probably as visisbly red as they are due to sexual selection. (Same reason we have hair where we do, why lions have manes, why some babboons have red or blue posteriors, etc.) Undoubtedly, the runaway development of complex speech had an impact on the flexibility, etc. of the lips, too.
So, in other words, a little of everything. 
And let’s face it, some people (and vegetables) just love their lips.