Here’s what happens:
The magician shows the audience four blue-backed cards, cleanly wiggling the cards between their fingers. The magician puts one card in their pocket or hat to remain in view so they can show the audience the old three-card trick. Magically, a new card is produced at the magician’s fingertips. The card is tossed away so the magician can show the audience the old three-card trick. The card returns again and again until the magician gives up on trying to get rid of cards. In a twist ending the blue-backed cards are shown to have transformed into red cards.
The gimmicks work cleanly so you can perform the effect both from stage and close up. Repetition is a trick you will find yourself performing again, and again, and again, and again.