X-Ray Tube - Mental / Street / Close Up Magic Tric

You display a metal tube with cap and 6 identical-sized, but different colored rods. The performer turns around, asks a spectator to place any rod in the tube, cap it, and hand it to him behind his back. He brings the tube to his forehead, and reveals the color of the rod inside the tube. The effect can be repeated, and everything can be thoroughly examined at any stage of the performance.