The magician introduces a small plastic box. He removes the lid and dumps out a small cube. The cube is shown to have a different color on each side. The spectator is invited to select a color, place the cube in the box with the selected color on top, and replace the lid. The magician turns away to allow him to do this. The magician faces the spectator once again and takes the box from the spectator. After concentrating on the spectator’s thoughts, he is able to correctly divine the chosen color!

Demo:

https://youtu.be/xTj_UErgM-g