Exactly... I have the sphere set at a tranparency of only 2 (so I keep the contrast). Then I use a lightdome outside of the sphere that with fairly intense light settings (intensity of 10 for each light is rather high if it had not gone through an almost black sphere). Now you see that the sphere is coloring the objects you place inside. So this technique makes it possible to use whatever material you want and still get the exact right results.