A figure or portrait doesn't have to be painted in realistic colors. Using unrealistic colors in an expressionist way can create dramatic paintings. Just take a look at the greens and blues used as 'skin' colors in this this self portrait by the German Expressionist painter Karl Schmidt-Rottluff.
To create an Expressionist range of skin tones, select the colors you'd like to use, then and create a value scale as you would do if you were using realistic skin tones, from light to dark. With this to refer to, it's easy to know what color to reach for when you want, say, a mid-tone or a highlight color.
