I used water soluble oil paints for skin tones: titanium white, yellow ochre, raw sienna, and burnt sienna and midnight black.
For all my sculpts I make four basic flesh types:
The basic flesh tone: 1 part yellow ochre, 1 part raw sienna, 2 parts burnt sienna, 6 parts titanium white
To get Asian tones: mix equal parts of yellow ochre to the basic flesh tone
To get AmerIndian: mix equal parts of yellow ochre, burnt sienna, the basic flesh tone
To get Black: mix one a touch the brush on midnight black about five times the amount of the basic flesh tone
These are either mixed with titanium white or diluted and applied for shading.
So to paint a Blade head, I used the AmerIndian tone for the base layer. Then, I shaded the crevices of the sculpt with the black tone and highlighted the sculpt with Titanium white and the Asian skin tone.
To paint an Asian Odd Job head--- more yellow, I used the Titanium white as a base layer. Shaded it with a mix of diluted Black and Asian skin tones. Then applied highlights using varying amounts of Titanium White and the Asian skin tone and the Amerindian tones.
To paint a Caucausian Carl Kolchak--- more pinkish, I applied a base layer of AmerIndian skin tone. Then applied a thin wash of Titanium white. Afterwards, I highlighted using a mix of the Titanium White and the basic flesh tone. Then, I did a dilute wash with the Asian skin tone until I got the look I wanted.