Portrait Painting by E.W. Harvey

Palette of Oil Pigments

Obviously, there is not just ONE correct way to mix skin tones, but here is what I do:

For flesh tones:

Mix a dab of alizarin crimson, a dab of burnt umber, and lots of titanium white.

For rosey areas: Use a tiny bit of cadmium red medium mixed with white.

For various shades of skin: To create the pale skin of a blonde or redhead, add white + a touch of yellow cadmium light.
For dark skinned people, add a little ultramarine blue and burnt sienna.
To create shadows on the skin add a bit of one or more of the following to the flesh tone: viridian, ultramarine Blue + alizarin crimson (purple), burnt umber, burnt sienna.
Experiment with what looks right for your subject. Note how the viridian and burnt umber mix below is a great match for the veins that sometimes show through the skin.

Regarding black or gray:

Many artists advocate adding a little black, but my first (and only) painting class was with an impressionist painter, who stressed that black was a no-no and so I am accustomed to using a combo of ultramarine blue & burnt umber, which is as black as I ever want to go.

My Palette: