Here's a photo taken in his studio. I can see terra verte (which I've also heard him mention in interviews), maybe cobalt blue, a sienna, and maybe cadmium? yellow. Not sure what the reds are. You can probably simulate his palette with umbers, ochres, and siennas, earthy greens such as terra verte, a couple of blues (maybe cobalt and ultramarine), black, white, and brighter yellows and reds (cadmiums) when needed. I have to say though, that I never dealt with powdered pigments, so I'm not sure about safety issues in dealing with pigments that may be toxic such as cadmiums.