I like the blackwall look on cars, the problem is most tires come with white lettering or a stripe.. mounting that on the inside it's still visible, so I was wondering if it'd hurt the tire to spray some flat black paint so you cant see the white?
Regular spray paint wouldn't be good for the rubber, although you would probably get away with it.
Different companies used to make a product called "tire black" that was meant to make old tires look new. It was basically a tire rubber compatible paint. I think it's now water based and used by places that sell used tires. You might be able to find some in a good car parts store. Look for "tire black".