That's beautiful! That's what I expect to see when with Render Quality: High. I'm glad to see it's not a problem for everyone.
Meee tooIsaac wrote:I think it must be OpenGL... I wish the Windows version optionally supported OpenGL.

I will consider the mystery solved for now, unless someone with OpenGL Grimrock has these color issues too. I'm a little sad DX9 doesn't have a solution (right?), but it won't stop me from playing - not a chance

Thanks all for your input and tests!