This person is the libero. It is the defensive specialist. It is not a captain or the center of rotation. The Libero is an Italian term pronounced LEE-beh-ro. (It is commonly mispronounced.) The job of the libero is to specialize in all defensive skills. They are required to wear a contrasting jersey and cannot block or attack the ball when it is entirely above the net height. At breaks in the game, when the ball is not in play, the libero may replace any back-row player without notifying the officials. The libero can then be replaced ONLY by the player whom they replaced. The international rules also state that they are not allowed to serve. "The libero may function as a setter only under certain restrictions. If she/he makes an overhand set, she/he must be standing behind (and not stepping on) the 3-meter line; otherwise, the ball cannot be attacked above the net in front of the 3-meter line. An underhand pass is allowed from any part of the court." I hope this helps. =) EDIT: 'S V' ...
The one wearing the different coloured shirt than the other 5 is the "Libero" or the defensive specialist.He isn't allowed to serve or to "dunk" and he only passes the ball and blocks it.He must have good passing and blocking skills.