You show a square cardboard panel. When you unfold it, it takes the shape of a rectangular tube.
You show the interior of the tube to be empty with red stripes. You place a blue silk in the tube and collapse it back into a square cardboard panel. When the cardboard panel is unfolded the color of the silk and the color of the interior change places. You now have an interior with blue strips and the silk is now Red.
This is an easy to do prop that packs flat and plays big. Silks not included.