This is a terrible example as the florescent light have tainted the true color.
You can get a pint of white latex paint at HomeDepot and have it tinted with just a little color. The background above is really faint powder blue. A light back ground bounces more light around in the tank.
In this tank I used a 2'x4' Bubble Textured floresent ceiling light defuser from HomeDepot cut to size. It's behind the tank.
I like this better as different amounts of room light will affect the background. Also, different amounts of light will shine through at various levels. I like that more than the solid color of my painted backgrounds.
I don't have a pic but, I've also used 5% "limo" window film. That will also have different light play so it doesn't look too uniform.