This is a very beautiful piece. I looked at it in larger form and tried to vision a color between what is present and mix that with some red and just use this color on the lips, just a little on the red. I don't know if this would work. Or just leave it be.
Otil, I have to say that I love all of your work... so it is difficult to chose. I am more in favor of painting though because your colors are always so beautiful too. However, if you are selling "prints" of your work on FAA then you could paint the original artwork and sell both versions (painted and unpainted) of the prints. Seems to me that might be the best of both worlds.
your painted versions are wonderful and showcase all the wonderful detail. I would paint it. Megan has an excellent idea in selling both versions as prints.