Three chips - one red, one yellow (amber) and one green - are all covered with a pocket handkerchief. The red chip is removed as the magician states, "Red is for stop."  Then taking out the yellow chip, the magician says "yellow means get ready."  That only leaves "Green for Go", The spectator now removes the handkerchief and to their amazement, the Green Chip has vanished, all that's left is a totally transparent disc.