I've just sketched this in between other sketches, filling up all the spaces in my sketchbook.
You have to ignore the half drawn upside down faces above and beside her!!
Excuse the spilt tea!
I have found sketching women with make up on surprisingly tricky. When you look at them, their mouths look very dark, but if you draw it like that, the sketch looks really strange. It is even worse if they are grinning! In a large A4 sketch, this sorts itself out easily, but in a thumbnail pen and ink sketch, sketching too many lines in pen quickly makes it look strange.
Seeing as I want to be able to draw everyone (particularly happy people), and I really like miniature sketches done with a 0.05 technical pen, I decided to do a bit more research on this. I experimented with sketching people with cheesy grins (my favourite sort of happy person) a while ago. But it really makes a difference once the subject has a lot of makeup on.
I think the answer is that even though we see someone has a lot of lipstick on, the actual value (darkness or lightness) of the makeup is not necessarily that dark. If you squint when you look at them, which makes it easier to judge the values, the lipstick often disappears. So, I think, in ordinary lighting, it is often best to sketch the upper lip just as very light, broken lines, without darkening them too much. The lower lip is barely marked, but you can tell how it is shaped because your mind continues the line started by the blackness at the far left and right hand edges of the grin. As in the two sketches above.
The sketch below shows how wrong it looks to darken the upper lip in a thumbnail sketch - when you see it you think you are looking at the inside of the mouth, not the intended lipstick, at all.