I Give to You......
What do you see?
Do you see what you are looking at?
I don't think you see it.
So, I'm going to tell you.
If you examine each of the set of lips, you should see that the upper lip is always a darker value than the lower.
This is my mother. Notice her lips have color but the lower is a lighter value than the upper.
This is a sepia print of Ashley. When her lips are relaxed, she has a thin upper and pouty lower. She is always smiling and 99.99% of the time she is showing teeth. (I don't do teeth)
You can easily see in all of these pictures that the upper lip is darker than the lower. If you have trouble seeing that, then look at lips with squinted eyes and you will see the difference.
Of course it is all about the light source. And generally, the light is coming from above even when it is coming from an angle above. The thing is, we don't realize that our upper lip doesn't catch the light and in fact catches a shadow.
Looking at the lips in profile gives you a better understanding of how it happens that the upper lip is always a darker value than the lower. So, when you paint or sketch, try using a darker value of color.
Now here is a little homework assignment. When you are watching TV, start looking at lips. I'm really sorry that this will run you crazy and you may see nothing but lips for a while. It is how we learn through observation.