Hats & Persons

• A, B & C are 3 persons standing in straight line.
• A can see B & C
• B can see C & not A.
• C is standing facing the wall & can't see both A & B.
• There is a bag with 3 black hats & 2 white hats.
• Randomly the hats are picked & placed on the persons.
• A person doesn't know what hat he/she is wearing.
• When A is asked for the color of his hat, he sees B & C & says 'I don't know'. B & C analyzes the response with care.
• When B is asked for the color of his hat, he sees C & says 'I don't know'. C analyzes the response with care.
• When C is asked for the color of his hat, he says 'I know... It is ____'...

What is C's hat color? How did he find out?