Correct but how? In this case you can (but you can't) see 2 objects inside a mirrored sphere. The bulk of the picture you see is reflection. Now if I made my centre sphere with a water material it would change the entire picture due to reflections. If I added an extra (water) sphere in front of the original, thus hiding the original it would just render as that and have minimum effect on the picture. Plus the title would be wrong. Some other materials work but I wanted a mono simple look. This to my mind deals with form and light not really colour or texture.