The magician displays three mummies each of a different color. The mummies are handed over to a spectator along with a small Egyptian coffin. The spectator is invited to select a mummy of his choice and secretly place it into the coffin. 
The tomb is them sealed and placed on the table
The other two mummies are hidden from view. This is done without the magician watching.
The magician faces the spectator and instantly reveals the color of the hidden mummy!