Mix yellow ochre with a small amount of red
Add a tiny amount of blue or burnt umber to neutralize the mix
Use more water for lighter skin tones
Add more yellow ochre for warm skin tones
Add more red for pinker skin tones
Add more burnt umber for deeper skin tones
Add a touch of white gouache if needed for highlights
Test the mix on scrap paper before painting
Layer thin washes to adjust the skin tone gradually