Thank you for all your suggestions. My intention is to export primarily to Photoshop, so I can produce quick colour illustrations. Currently I manually paint each surface in SketchUp with bright or contrasting colours,before I export a 2d file. I can produce a mask of the surface in Photoshop it is just slow. I had hope some one would have a script that would automate the process in SketchUp. Colour by layer name or entity maybe. The ability to make Alpha masks when exporting would be great. I have looked at Piranes,it looks very complex I will give it a try.

Is there a ruby script that will color the 6 faces of a cube different colours, or a complex model. I would then export the file in 2d to photoshop and create simple mattes from the colored faces for painting.