WAYyyyy too easy for friendly fire to happen in this game. The way they did it in the old days was to give people colors to know your team mates. Colored, armor, or preferably, colored clothing worn OVER armor, would be preferred for distinguishing friends and enemies. Give some tailors something important to do.
Imagine, waltzing in BOB is King territory and seeing everyone there wearing the royal orange. You could quickly tell inhabitants from non inhabitants. Likewise, some black - ops could go in wearing stolen or premade clothing to be wolf in sheep's cloths