A hinged pair of plastic plates are opened showing a red spot on one plate and a blue spot on the other. The plates are closed and the spectator is asked on which side is the red spot. He can't make the right guess as the spots have changed colour to black and yellow instead. After the trick, the plates are handed for examination. 
 
Condition Notes:  Complete with original instructions. Both the packaging and instructions show some storage and age-related wear, but everything remains intact and usable.