No one has ever liked this idea to my knowledge, although I've brought it up several times........
The purpose of a background is not to draw attention to itself, but to draw attention to the aquascaping and inhabitants (afterall, thats where your money goes). Bright interesting backgrounds take attention away from what's living in your tank. Black painted backgrounds are good, but if you have fish that have black in their coloring (even a little bit) the fish tend to get lost as they blend in with the black background. I have two Onyx Mis-bar Clowns in my nano with a black background, so trust me, I know this is true.
Years ago (when I did a background) I painted the back a medium <span style="color: dimgray">dark gray color</span>, and found that in contrast to the fairly drab coloring of the background, my fish's and invert's colors just seemed to pop! Orange looked more orange, blue looked more blue, lines were more defined and everything in the tank looked more colorful and healthy. In the twenty plus years I've been doing this, I think that is the best background I've seen.
Another idea I might try in the future is to lay the empty tank on it's back, smear silicone on the back glass and use a tank substrate (same or different from what I use on the bottom of the tank, haven't decided yet which would be best) to cover the tacky silicone.
Possibilities abound, but it's really something you want to get right before you set it up, as dealing with a new background on a functioning system can be problematic.
Food for thought.....