Black Hats and White Hats

In a dark room there were 3 black hats and 2 white hats. Three people, A, B and C were asked to go inside the dark room and put a hat on and then leave the room to stand in a queue. No body could see the color of their own hats. A stood in the front so he could not see B or C. B could see A but not C and C could see both A and B.
When C was asked if he could tell the color of his hat, the answer was "no." And so was the answer from B. However when the same question was asked of A the answer was "yes."
What was the color of A's hat? How did A figure this out?