The magician shows two decks of cards in their boxes, one red, one blue. He has a deck selected and in an instant the box disappears living only the cards in his hand. The box is removed from his pocket.
Next he shows the cards blue cards front and back and tosses them onto the table. Instantly their backs change to red!
The red box is opened and it now contains blue cards.
Henry Evans used this trick in world champion performance at FISM 2000