I must be losing it, as I can't figure this out. What kind of shading type or shader do you need for nParticles to respect the attributes in the shading tab? I tried with cloud (s/w) and nothing I changed in the shading tab affected the render (mental ray) and then I tried with spheres and a surface shader applied to the particles and again, nothing I change affects them.

Put another way, what is the proper way to render per particle attributes with mental ray? And ideally without being influenced by lights. (Use lighting is unchecked, but it's greyed out anyway).