Spray painting perlite will do a couple things:
-Make it less porous and change its physical properties
-Introduce a potential source of toxins into your system. If you don't take paints/solvents seriously, google 'hydrohut syndrome'... that wasn't even in CONTACT with actual plants...

Vermiculite is brown and less visible as a waste product. It's not as good as raw perlite, but hella better than painted perlite.