You can paint acrylic the exact same way as you paint glass. You can use a roller, spray paint, air brush, paint brush. You can use spray paint or acrylic paint. The difference is getting the paint off. Glass you can use a razor and scrape it off without worrying about scratches. Acrylic you can not. You can still use a razor, but you will have to buff it afterwards.
Starfire to acrylic...acrylic is still clearer and does not distort like glass. Glass, starfire or not distorts the view. A lot of people get dizzy looking through glass for long periods of time due to the distortion. Looking into any acrylic tank, it looks like nothing is there as well. Starfire is clear no question, just won’t ever be as clear. Not an outdated fact, still holds true, they just improved glass clarity. Still, there are impurities.
Can you please post a picture of your background so we can see why it does not work? There is no reason that I can think of why it would not work.
Pics of my tanks are in several threads but the easiest one would be the "new tank pics "thread. Has a deepwater jungle background in shades of green blue and turquoise. Its painted on and sealed with white plastic material. 3D printed quality. Company I ordered from has 50 backgrounds and you can custom order one or even put your picture on the back.
The difference in starfire vs acrylic is not perceptible, really. Yes, on a molecular level there's some small difference but that alone isn't that big a deal to the average cluck. Biggest thing would be the fused edges of acrylic making it more clean and seamless. But some people like the framed look, especially with black silicone seams. If people get that dizzy looking at glass they're dizzy to begin with. Nobody ever looked at my tanks and hit the floor.
Acrylic can absorb small amounts of chemicals in the air, (molecules porous) glass does not. Say from paints/cleaners and the like, petroleum based products if your tank is in the basement and you do household projects. Fumes can be an issue.
At the end of the day I've seen muffed up glass tanks and muffed up acrylic tanks. Its just what features are important to you.