Four prisoners are standing in a line, all facing the same direction. A wall separates the fourth prisoner from the other three. They know there are two blue hats and two red hats, and they are each wearing one. Prisoner 1 can see 2 and 3. Prisoner 2 can see 3. Prisoner 3 can see only the wall. Prisoner 4 can see nothing. Who shouts out their own hat color first?