Great comedy routine that plays great with a young audience!
You show a red crayon, a yellow crayon and two blue tubes.
The volunteer picks a color of their choice and you take the remaining crayon.

Both you and the volunteer hold the crayon in your left hand and slide the tube over the crayon and place your right hand on top of the crayon.
You then flip the tube so that your left hand is now on the top of the tube.

When you lift the tube, you see that the crayon is still right side up, but the volunteer’s crayon is upside down.

You end up with the same result even when you exchange the crayon with the volunteer.

Tube is about 12 inches tall.