Display a face-down, red-back Bicycle card.  Hold it near a light source and a black spot card is seen through the back of the card.  Turn the card face up and reveal that it has transformed into a red Ace.
 
The value of the black spot card varies.
 
“Tom Frame makes a very nice Transparent Card.  It inspired me to work out a killer faux card cheat routine and you can get it for free if you buy his remarkable card.”     - Bob Farmer