The magician displays a large white plume, which he pushes into a silver tube. He asks the members of the audience to call out a colour, and, peering into the tube, announces that the white plume has now changed to the chosen colour, say, red.

He now asks for another colour, and, peering into the tube again, states that the red plume has now become blue! This state of affairs continues just this side of anarchy, when he declares that it is now his turn to choose a colour and he is going to choose . . . WHITE! So saying, he pulls out the white plume... 

Would the audience like to see a re-run? The business is repeated, when suddenly the magician stops and says, “Oh, you want to SEE the colours? You want to see yellow and red and green and blue and pink? Ah! There’s a problem. You see I can’t actually show the colours, but I suppose if I could, it would look like this and the tube would be empty.” As he says this, he pulls out a gorgeously coloured plume and shows the tube to be completely empty!

Simple, but oh-so-effective!