Open a long case and show five different colored brass Poker chips. Place them on the table and ask the spectator to choose one of them. (No force). Stack the chips and tell him, that you have a prediction an the back of the box. Turn it over and show a mirror. Hold the mirror close to the stack of chips, and a mirror reflection of the top chip is shown in the mirror. Spectator not impressed....
But let him take his selected chip. He will find your signature on the back, and all the other chips have only white surfaces. Everything can be examined. Right away you can repeat the effect. Let the spectator just THINK of a color. Then you put your initials on the back of one of the chips. When turned over, your initials will be found on the chip chosen!
