performance:
The spectator picks a card. After the card is back in the deck,
the magician shows, that the choosen card has changed its back color. The card is put on the table and the spectator picks a second card. After this card is put back in the deck, too...
nothing happens. There is no card with a different back color in the deck. Did the trick fail ? No, the card on the table changed into the card, the spectator picked the second time.

the trick:
You need a regular deck of cards and a card with a different back color, e.g. the Ace of spades. You take this aces and the matching ace of the deck and put them at the bottom of the deck. The ace with the different back color is now the bottom card. Now you´re ready to performe the trick.
You have a spetator choose any card of the deck (don´t show him/her the ace). Now you give the deck some cuts. When you go through the deck and you see your ace ( that one with the other back color) you cut the deck, so the ace is on top of the deck. Now you say, that the card of your spectator has changed its color. You perform a double lift, and show them their card. Now you put the card face down on the table.(The spectator thinks, that it´s his/her card) Now the bottom card is your second ace. Perform a hindu shuffle and ask the spectator to say stop, when he/she wants. When he/she says, you show him/her the ace, which is still at the bottom and cut the deck again. Now go through the deck. Of course you won´t find a card with a oher back color. Now you show the spectator, that their first card has changed into the ace and turn over the card on the table.