Tell-a-Vision Box by Royal Magic
Discern their thoughts!
Hand the participant a cube and a small box into which the cube fits snugly. On each of the cube's six sides is a different color. The participant selects one color, and places the cube into the box, while the magician's back is turned.
Handing the box over to the magician is all it takes - the magician instantly knows which of the six colors was selected!
Easy to do! No sleight of hand. All the props are examinable.