Only difference is color. Price is based on supply and demand. When there's a bigger demand for black, its price goes up. When there's more silver ones hanging around unsold, their price goes down. I wonder why Canon still makes the silver ones though. Maybe because the Rebels have traditionally been silver from the beginning when they were simple film SLRs.
Oh, I dunno. My old silver Rebel with black battery grip used to draw some attention and compliments while the guy next to me with the basic black Nikon got none (even though he actually had the better camera). ;)