I used to work in pastels instead of oil paint. It was convenient when there were little kids around the house. I learned a lot about color using pastel. It's an addition and subtraction process, adding color, restating areas, layering cools on top of warms, finding the warm tones again. With pastel, you can't mix the perfect color. You have to make the colors you have work. Now, when I'm at the point in the painting process that I've reached with Darnell, I paint with oils the way I did with pastel. I'm adding thin veils of color, perhaps getting too warm, then  cooling it down with a bit of titanium mixed with the color I'm using. If it gets chalky, I'll go back into it with a glaze of a transparent color. I'm adding and subtracting until I get as many of the subtle nuances of the skin color as I can.