Why does one player on a volleyball team have a different color jersey than the rest of the teammates? I notice that this player only plays on the back row and never plays in the front row, and that this player is often shorter than the players that play in the front row.
The player with the different coloured jersey is the "libero" - a specialised defensive player who is able to be freely substituted for any back court player. They can never rotate to the front court (if that would happen, the player they've replaced must re-enter the court), engage in any kind of attack from above the height of the net (even a back row attack) nor serve. There's also a restriction that means that if the libero performs an overhand set from the front court, the ball cannot be attacked above the height of the net - this is to prevent the libero being used as a back row setter.
As they can never perform an attack nor block, the libero doesn't have to be as tall as other players - although everything here is relative: the two liberos for the 2014 world champions, Poland, were 184 cm and 188 cm.