So I have a 30gal terraium and I was thing of blacking out the sides and the back. Questions:
Does it add any comfort for the ball? Yes - a lot.
Have you done it? Nope - my API T8s only have a glass front though - the rest of the material is black already.
How to do it? Anything from black construction paper taped to the outside to the stuff you can buy for aquariums (again - on the outside).
Is it worth it? Only if you prefer your BP to be comfortable.