Why? Black goes with everything. Black will go with your next bike. Velcro comes in black. Flat black spray paint comes in black. Black is hard to see, so thieves won't be attracted to any bling. And finally, black doesn't reflect the sun so you won't get glare in your eyes while riding. Sorry, I don't care if your sweet baby is blue, the blue stuff will be ugly on your next bike. Think about it. Gonna buy one of those orange ZX-10s? Blue goodies on an orange bike? PULEEZE!
Black paint? Here's the hot tip. Rust-oleum Textured spray paint. It's available at Lowes or Home Depot. This stuff is terrific. It produces a lightly sandy finish that closely matches the plastic surfaces of lots of motorcycle plastic work used inside the cockpit. It's resistent to poor painting methods, resists sagging, and is very forgiving of bad surface prep, scratches, and the like. It also doesn't show fingerprints or wear.
Here's a link to the product.