Paint in a neutral colored tone over the entire canvas to reduce the brightness of the white. Use fine-bristled art brushes for best results. Use a cool or bluish gray color for the background area around the face. Under-paint the face area using burnt sienna with a little cadmium orange added. Paint the darkest shadowed areas of the face or figure with a thin coat of dark umber earth tones to establish the tonal relationships of the picture. Paint in all the darkest shaded areas first, adding a little ultramarine blue for coolness. Draw with tones and later paint your skin tones on top of these dark colors.
Paint in the mid-tone areas next using lighter earth colors such as raw sienna or yellow ochre. Keep in mind you are doing the under-painting, working out a chiaroscuro effect of contrasting shadows with areas where light is falling on your subject. Add tints of blue and purple to your shadowed areas to keep them cool.
Paint in the lightest areas last, adding touches of titanium white to the yellow ochre and raw sienna. Warm the brightly lit areas of the face or figure by adding slight amounts of light cadmium red or rose madder. Apply your paint in thicker layers as you paint in the lightest areas.
Mix your final layer of skin tone paint starting with a base mix of titanium white and adding touches of red and yellow. Observe the skin tone of your subject and try to match it. Blend the paint to fill in the gaps in your under-painting, letting it show through in some areas to unify the painting. Add bits of blue and a tiny amount of green in the deeply shadowed areas. Keep the relationships balanced and harmonious between light and dark and cool and warm colors.
Paint in the highlights as the final step in your painting. Use small touches of white with a little orange or yellow added to mimic the effect of light reflecting off the brightly lit areas of your subject. Use pure white to paint the tiny reflections of light off the eyes of your sitter.