I agree about the deeper red. I think that a dark blue and dark red would look awesome together. If you are still worried about it looking odd together, what about a lighter blue. Of course time of year could also determine other colors that may or may not be "appropriate".
Completely off topic but have you looked at cake toppers of firemen and their brides, some sites I have found while looking for military toppers had them, I can't remember off the top of my head, but you could always "google" it :-P.