Black shoes and belt are traditional, can't go wrong items with any dark suit, be it blue, black, or grey. They will never be out of style.
Brown shoes and belt are more faddish: they are considered "in" today, but won't always be "in."
When deciding between black and brown remember that you want to look like the interviewer might dress if he weren't in uniform. That way he will subliminally think "Yeah, he looks like one of us." So if you think your interviewers will be young, 25-30-ish guys then maybe brown is the way to go. And if you think your interviewers will be middle-aged guys, then black might be the best choice.
The belt must be the same color as the shoes; never, ever mix black and brown. And for God's sake: no white athletic socks!