In this Game, your color and Enemy color should match in order to damage and kill them. You can change your color during Battlefield by pressing E, to avoid enemy attacks, so do your Enemy can, Each time you kill your Enemy, you will be assigned a new color depending on your fate, it might not get changed if your are lucky. But if your color changed and the opponent has same color it can kill you. So To kill your opponent you are giving up your Color.