Portraits aren’t something I do too often, but every artist on any level should have at least an understanding of how to mix the effects of various light sources hitting flesh. There really is no “flesh” color right out of the tube of course. What type of light and how much light hits the subject affects on the color of skin most of all.
Sometimes it’s just good to start very basically, with a tiny amount of red, a bit more yellow, and a pile of white for a caucasian skin color and go from there.
After taking a portrait painting class years back, I adopted a variation of the instructors palette and added colors from a few other portrait artists I admire to come up with the palette(s) below. Among the colors used are Burnt Umber, Raw Sienna, Yellow Ochre, Cad Yellow Medium, Cad Red Light, Ultramarine Blue.
Here is the portrait I painted from the live model in that class:
As I stated before, depending on how light hits the subject, any number of colors could be used. For the darker-skinned races, more of the umbers are used, but again, light has a lot to do with color choices.