Die Vison by Magicbox

In this version, you show a cube with a different colored spot on each side. you also display an opaque box.
There is NO WAY to see through the box! You turn your back and ask an audience member to think of one of the colors and place it face up in the opaque box. The box is handed back to you and you can instantly tell what color they chose! This can be repeated many times and each time you are able to demonstrate your powers of X RAY VISION!