GI hair demo Pixar's Renderman

Someone asked me for a quick demo of the last shader.Here is a standard hairball from the shave & haircut package. Now as you can see none of the background color is brought into the calculation. It looks as if the hairball is just composited on the background.

Simply lighting with the background image gives us a little better looking hair. There are no scene lights in this image just a back plate.
To be honest the light position needs tweaking and there are no shadows etc. But its a quick way to get ambient occlusion and color bleeding effects on the fly. Looks even better when your hair moves from room to room and the colors change appropriately.