Maaz,
The effect is that a spectator thinks of one of the 6 colors on the cube. Whatever color they are thinking of, they put the cube in the palm of one of their hands with the thought-of color uppermost, and then cover the cube with the other hand being placed on top. All this time your back is turned, and you can be 50 feet away or more, or even in another room. It would be impossible to see the cube or what color is uppermost even if you stared at their hands, as the cube is completely covered. Nevertheless, with your back turned the entire time, or even from 50 feet away with your back turned, you determine the correct color. I like to have them put the cube underneath a coffee mug or my chop cup with the thought-of color uppermost while I am 50 feet away with my back turned, or in another room, and I can immediately discern the color. This can be repeated with other spectators, or as many times as you want.