I used a lot of wet blending for the skin and a bit of glaze medium for all my paint to get the desired skin tone.
I glaze the recess area with an actual purple (Xerius purple) to get the purple shade. For the underbelly skin it was a mixed Stormvermin fur and Starken Green, then actual Starken green, then Druchi violet shade for the recess areas, then a very light glaze of Rakeath flesh, agrax earth shade to darken the skin and then a bit more Rakeath to highlight the top areas.
for the top skin I use, stormvermin fur, dark reaper and nuln oil, and then a light touch of Thunderhawk blue for the highlight