As tested with the [Umbra Turris] Orc Warband, I airbrushed the miniatures with a purple basecoat of 1:1 Molotow #233 purple violet and Molotow #043 violet dark both as an undercoat as well as an undertone, the reason why I did not choose my normal black. If my guestimation is not too far off, that mix is on the opposite side of the color wheel of the main skin color, Golden High Flow - #528 Green Gold.
This was followed by a zenithal airbrush step of Liquitex White Ink.
Next I applied the main skin color, Golden High Flow - #528 Green Gold, which I thinned 1:1 with Golden Airbrush Transparent Extender. When sprayed on, the zenithal still shows through, providing the first level of color modulation. Here is also the reason for the purple rather than black basecoat.
From below, in an opposite zenithal (nadiral?) layer, I airbrushed a darker green, Golden High Flow #577 Phtalo Green (Yellow Shade), thinned 1:4 with the extender medium.
For the highlight color to really pop, I added another white zenithal from directly above the minis, and some choosen spots (like when directly from above did not hit the face enough, or the belly).
The final layer then was a 1:4 mix of Golden High Flow #587 Light Green (Yellow Shade) and extender medium.
