Lips are such an important part of the face when painting a portrait, it pays to take extra effort to get the color right. While the color of lips change from person to person and in different lighting conditions, you can use a basic formula to get you close and make color adjustments based on the particular circumstances. The trick is to go slow, measuring results on the palette against what you see. The other factor is that you will mix two base colors — one for the upper and one for the lower lip. In general, light comes from above. Because of this, the lower lip, facing upwards, is typically lighter in tone. You can use the same base color, adding a touch of white to the mixture for the lower lip.
Things You'll Need
Paint (acrylic or oil): quinacridone red, yellow ocher, white, terre verte
Lay out one-half teaspoon of each color on the palette.
Mix two parts quinacridone red with one part each of yellow ocher and white on the palette. Mix until there's no broken color (i.e. the mixture is uniform). Use the palette knife for blending.
Dip the palette knife in the terre verte. Pull it out. Mix the terre verte remaining on the palette knife into your mixture. Again, mix until uniform.
Swipe the palette knife across the top of the mixture. This leaves a layer of paint on the back of the palette knife. Hold the palette knife, with your mixed color toward you, and point it at the lower lip of your subject (model, photo, or other source). This allows you to see the paint color clearly against your subject.
Compare the mixed color. Add tiny bits of color to the mixture on the palette to make corrections. Use the technique you used for the terre verte so you don't add too much at a time. To enrich the redness, add quinacridone red. To lighten the mixture, add white. Yellow ocher will move the color towards orange. More terre verte will make it a bit darker and more neutral. Correct until you are satisfied with the hue.
Scoop out half the paint mixture. Lay it on a different part of the palette. Add tiny amounts of white, mixing and testing against the lower lip your subject, until you match the hue.