Mine are black right now. They are ok, but I am going to try silver right now. Mine are on a teal car so I am extremely limited as to what colors wont clash.
I painted mine silver only because the stock SVT color was silver dacromat. I used silver high temp engine paint since I could not find any silver caliper paint locally.
That said about why I chose silver, gloss black always looks good and is always a safe color. Black caliper paint is easy to find. Even when it's dirty it still looks good.
Unless you are trying to make it look somewhat like an SVT, I would go with gloss black.