All right, in continuing this work in progress, I have finished the first paint layer, also known as Imprimatura.
Traditionally in oil colors, one would use Red Ochre, Yellow Ochre Light, and Ivory black. Not all oil colors are available in acrylics, so I have tried to come as close as possible.
I have used Naples Yellow, Ivory Black, a pinch of Red Oxide and Titanium White. This finished layer should have an olive hue, which I think I have achieved here.