Here is an example of surface_color and mean_free_path and what effect they have on the final result.

 

Top Row : Mean Free Path 0.1

Middle Row : Mean Free Path 1.0

Bottom Row : Mean Free Path 10.0

Column 1 : Surface Colour 0,0,0

Column 2 : Surface Colour 50,50,50

Column 3 : Surface Colour 100,100,100

Column 4 : Surface Colour 150,150,150

Column 5 : Surface Colour 200,200,200

Column 6 : Surface Colour 250,250,250

TemplarGFX
3D Hobbyist since 1996
I use poser native units

167 Car Materials for Poser