Effect

A spectator of any one of five playing cards, which he gets to hold. A paddle bearing six different-colored spots on each side is shown. A color is chosen and the matching spots vanish from both sides of the paddle. 

You bring one of the spots back but one stubbornly refuses to reappear. 

The spectator turns over his thought-of card to find the missing spot stuck on its back! Everything is examinable.