I was thinking about doing a dark blue acrylic sheet and backlighting it, public aquarium style.
Way to think like a freshwater enthusiast! They do stuff like this all the time, us reefers are due to try it.
Being that I once scraped black spraypaint off the back of a used 125g tank, I'd never paint a tank unless I felt I had no reasonable alternative. It's just such a pain if you want to change it down the road. Maybe that wouldn't be an issue for other people but it made me think about alternatives.