If you are using IDL, the Ambient_Occlusion for materials is disabled by default. You can force it on with the lights and shaders.  Too much AO can give artifacts in your render, so light based AO is not generally used with IDL.

The RGB system supports a large number of possible colors (256256256=16,777,216) but I am not sure how close human eye can see any difference.  You can also add color effect out of that range using HSV node.