That's something that I've always wondered about and based on when we see them wear them, I can only guess that the navy blue uniforms were for “lighter busts”; we only see them used in the montage, and they are only doing light work, nothing like busting Gozer or Vigo. So now the next logical question is what the hoses are used for. My guess would be that they inject some sort of “ecto cleanser” in case of something horrible happening. Of course this is only a guess that has nothing to back it up except for the fact that we never see it used and there doesn't appear to be any wires inside it for it to be an electrical connection. In reality the costume designers may not have had a logical reason for them, but just wanted to add another accessory to the outfit.