Three prisoners

Three prisoners are waiting in a single cell. The jailer comes in, and shows the prisoners 5 hats: two red and three black. He then turns out the lights, puts a hat on each prisoner and puts the other two hats in an opaque box. The jailer tells the prisoners that if they can correctly guess the color of their own hat (which they will not be able to see), they will be set free. If they guess wrong, they are executed.

When the lights go on, the jailer asks the first prisoner what color hat he has. The first prisoner says he cannot tell. The jailer asks the second prisoner what color hat he is wearing. The second prisoner says he cannot tell.

Then the jailer turns to the third prisoner. The third prisoner is blind, so the jailer is completely surprised when the third prisoner says, ”My hat is colored ...” What color hat was the third prisoner wearing and how did he know?