my two sense on the black v. grey. If you're going to get the black, get them with the brass studs. The brass makes that bag in my opinion. I actually looked at both at Barneys and the silver studs get lost with the heavy and dark nature of the black leather. And since the silver is dull and not shiny you don't see a really big contrast as you would with the brass. As for the grey...words can not describe how perfect the grey leather is. I'm not just saying this because I'm in love but it is always much much harder to find a grey bag that a.) isn't suede and b.) in the correct shade. Essentially that's what sold me on the grey. While the black is Ah-mazing I know I would have kicked myself for not getting the grey.
Also the silver studs go MUCH better on the grey. What's neat is that the silver actually reflects off of what you're wearing so for instance if you pair your bag with say, gold shoes, it'll pick it up and it looks great.
Either way, whichever color you get you can't really go wrong.