The solution to the puzzle

The man who calls out is Number 2.

Why?

After a short time, Number 1 has not shouted out what colour hat he is wearing.
Because of this number 2 knows that he cannot be wearing the same colour hat as the person in front of him.
If he was then number 1 would see two black hats and would therefore know that his hat must be white.

Armed with the knowledge that :-
He isn't wearing the same colour hat as the man in front.
The man in front is wearing a black hat.
number two can confidently shout out that the hat he is wearing is white. Easy wasn't it!