The magician displays an empty black can with white spots, and two silks - one black, and another white.
"This is a white silk dyed black, and this is a black silk dyed white" he says, "and this is my black and white transformation tank, which will make the white silk black and the black silk white"
The two silks are now placed in the can, and again removed. "There, you see... the white silk dyed black is now white, and the black silk dyed white is now black again!"
This is repeated until the audiences releases you are pulling their leg, and tell you so!
You appear hurt at this accusation of trying to deceive them so blatantly, and offer to make the transformation a little easier to follow. The silks are replaced in the can.
You now pass your hand in front of the can, wiping off all the white spots. The can is now completely black. The 'spots' are tossed into the can. When the silks are now removed, the two silks are found to be spotted.
"There you see... the white silk dyed black which is now white has the black spots, and the black silk dyed white which is now black has the white spots!!!"