Three "wonder blocks" and an empty tube are shown. The magician passes the blocks through the tube in this order: Red, white and blue. But when the blocks come out of the other end of the tube, they come out in a different order: Blue, red and white.
The spectators can put the blocks through the tube themselves - they never come out of the other end of the tube in the same order!
Puzzling to the nth degree. Very easy to perform. Complete with all necessary props and detailed directions.