Time is the resource which is always in deficit and you don`t have much of it in combat, you need to recognize friendly or foe players in a moment and take the decision. And your friends have the same problem. The prevention of such problems is needed.   

The old method, checked by time - is Friend or Foe armband it`s cheap,simple and fast method. It`s necessary bothly in airsoft and paintball.   

This armband is modern modification of old-gen one, mounts at velcro-panel, not for shoulder loop. This armband is very popular in different SF units