Achieving the desired skin colour is a really tricky process when creating portraits, but here’s a quick trick for assembling a basic palette that you can refer to time and time again.
Choosing a midtone will depend on the light source you plan. For standard scenes, it’s safest to go with a typical beige.
When picking highlights and shadows, remember that their hue should differ from the hue of your midtone.
After you have chosen the highlight and shadow colours, eye drop them. With those colours selected, apply some strokes on top.
Review all the colours you created and choose the boldest combinations that strongly differ from each other.