Color Changing Pyramid

The magician shows the audience a flat pyramid. One side is yellow; the other red.
The magician folds up the panels to create a yellow pyramid, and then pulls out lots of yellow silks.
Now the magician flattens the pyramid, creates a new red pyramid, and proceeds to pull out a lot of red silks. Surprisingly the last silk is blue, so he unfolds the pyramid and shows that its color has changed to blue!

The pyramid folds into a small flat triangle for ease of transportation and will mystify even the most professional magicians!