I'm almost positive that it was a mistake. Could have been just to show that there could be 2 possible colors like originally planned for AT&T but obviously we all know the problems Apple had with getting the white color correct..
And now that it only shows the black model I think it is safe to say it will only be available in black.
Maybe one of these days Apple will offer custom cases, kind of like custom engraving. You could order an iPhone or an iPad with your choice of sports teams or something. Of course, no Florida teams would be allowed. They are all sucky.