The cool thing about practicing with reference is that you understand skin has multiple colors. In this case, I didn’t use brown, for instance. The pallete was stuck in the blue/purple area of the color wheel and, yet, we can have an idea of a dark skin color!
Practicing colors and portrait during 2 weeks everyday have made me understand what I’ve always heard artist saying: do not use pure white for light. do not use pure black for shadow. In order to get a realistic essence, saturated colors do the job. Sometimes we think a certain area of the shadow is brown or black, but wait! No, it’s a dark saturated blue or red or purple. It depends on lots of things, especially light.
There are influences of nature and physics around us and if we take our time to observe them, our painting improves a lot! I guess 50% of the time, “improving” is to observe. The other half is applying what we see. So never make fun of someone who finds two or three minutes to look at the sky with no apparent reason: they must be artists :D