You can also have refraction and get fairly good imitations of translucency. Look up refraction in the help files at Pixologic.
For this they must be on the same layer however and the layer baked. You can adjust through the rgb slider or you can make many modifications with the normal material (no Matcap) with transparency and through coloring diffuse. Also reflections can be added.
The hollow look of the top sphere is done by using negative transparency in the material which is the plastic material in this case.
I don't see these used much in renders here but full details are in the documentation.
I have not been posting much but I'm enjoying your progress on this.