Painting the back wall

[Black Phantom]

If you want to paint it you have to prep it right. This means the glass has to be perfectly clean. Use vinegar and water for the first step. Use a non lint soft cloth. An old cotton t shirt works well.
Once you are done, wipe the entire suface with with either acetone (do not touch anything plastic and very high odor) or denatured alchohol.
Use a new clean cloth and don't touch the glass with your hand.
Once you are done use a quality Latex paint and a roller. Take your time and it should come out fine.
Brushes pull the paint and a cheap brush will leave streaks. That why a good painter uses quality materials.