The first step are the base colors, I use at least two. With several base colors I can keep lines visible that do not belong together:
(The nose has also a slight color difference to the rest of the face, but it’s hard to see)
Second I’ll add natural tones (red, orange, yellow, green, blue) based on the base color (Just the base color but with the hue changed to the different one)
Then I’ll add the first layer of shadow (Darkest color of my palette):
Then the first layer of light (Not the lightest but still lighter than the base):
Then shadow with a color that was not as dark as the first but still darker than the base:
Then light again (Lightest color of my palette):
Next, shadows on the spots where not so much light gets (darkest color on Multiply)
Then a bit of red (on the same spots where I’ve added the red on the first layer)
Then some highlights (Base color on Addition)
And some final highlights with one of the lighter colors (depending on which looks better) on Addition
Here’s the color palette I’ve just for the skin btw
