Two cards are folded into quarters. One is red-backed, the other is blue-backed. The cards are placed behind your back and mixed around. The spectator is asked to guess which hand has the red card and which has the blue card. Obviously, this is just a guess as both cards are hidden in the hands.
You offer to make this a lot easier, both folded cards are placed in the left hand. The red card is openly removed. Now there is no guess as they can see the red card. In the blink of an eye, the red card changes to the blue card. You really have to see this to believe your eyes.
You offer to repeat this a second time. Now you openly remove the blue folded card. Once again, they change places.
Next you offer to show them how this works. The red card is removed. Leaving the blue folded card in the closed hand. the red card is simply touched on the back of the hand, the two cards instantly change places.
Now for the killer climax. You state obviously you cannot show you both cards at the same time. As this is said you show the two cards, the red in the right hand and the blue in the left hand. Now it's impossible, as they can see both cards. The hands never hide the cards or come together. Visually the two cards change places in the blink of an eye.
The two folded cards are shown on all sides. They are unfolded, shown back and front and put away in the wallet, all reset and ready for your next performance.