I'm sure you could. I've also read about painting the inside of hoods. You can pick up aluminum reflectors that are quite efficient at redirecting most of the light down into the aquaium. They're quite cheap, and would work much better (IMO) than painting the inside of the canopy. I'd personally be really careful in what paint you select if you decide to paint though, seems like a potential fire hazzard. I've never tried it though.