I've just finished painting 3 of my tanks blue in the back. I used to use a background taped to the back but it didn't look clean. Tape on the sides and also water gets in between the background and tank doesn't look good. As far as painting the back of the tank and sides, most believe that the breeding fish will feel more secure.
If it's linear to sight, then painting would really stimulate breeding, but most of the times water parameters, stress levels, live feeding, rainy/sunny season do the trick.
On my breeding setups that sit side by side, I paint three sides.
Does a couple of things. Gives the fish what I notice to be a bit more "comfort". Also eliminates then seeing the fish in the tank next to them. Some of my breeders seemed to be distracted with the fish next to them until I painted them.