In a blue deck of card you show that one card is an odd card. It has a red back! You take out the red backed card and show it freely. The spectator can feel the card, there is nothing wrong or special with the card.
The red card is put back in the blue deck by the spectator and the deck is being shuffled. The magician makes a magical pass over the deck and when the odd card is being removed from the deck it has changed to a BLUE back as well (and there are NO DUPLICATES seen).
However, the card is ALWAYS going to be an odd card, because when the deck is now turned over, the ENTIRE DECK has changed color!
Strikingly odd is a very surprising routine with a climax were the audience goes wild!