The Mislabeled Boxes Riddle

There are three boxes. One contains 2 black marbles, one contains 2 white marbles, and one contains 1 black marble and 1 white marble. The boxes are labeled BB, WW, and BW. However, each box is labeled incorrectly. You may take one marble at a time out of any box, but you are not allowed to look inside. What is the quickest way to determine the contents of each box?