This is a girl I know very well. She has beautiful skin.
I narrowed my usual range of colors to paint the skin tones on this one. Cut alizarin crimson and the usual ultramarine, cobalt, and cerulean blues from the lineup. I cut even the cadmium red.
So I built the whole face with only white plus 4 colors: Yellow Ochre, Venetian Red, Raw Umber, and Viridian. Of these, I used Viridian the most (it’s a weak mixing color). I mixed dozens of colors with these, all with a generous heap of Galkyd added.
My best advice is to cut any out-of-the-tube colors from your palette. Just get rid of them! Make it a rule. In fact, you’d do well not to even use umbers or siennas, because you can mix your own umbers and siennas and they’ll be richer and more under your control. I use raw umber only when I’m mixing dark colors, and I use raw sienna only to make greens and blues earthier or warmer.
Also, if a color mixture has lots of white, keep it thick and opaque. I probably used more Galkyd than I should have, but that was just to keep the brushstrokes clean. Another solution for getting clean, smooth, dynamic brushstrokes is to lay down a wet layer of Galkyd + stand oil + turpentine and then paint atop that layer with thick paint (no turp, no medium). Definitely try this technique if you’ve never done it before.