Observe the rainbow-colored interference patterns. The patterns will change as you bend, twist, or press on the plates. Notice that the patterns strongly resemble the contour lines on a topographic map. Place the red plastic between the light source and the plates. Notice that the patterns are now just red and black.
Light waves reflect from the surfaces of two plastic sheets separated by a thin air gap.
These light waves meet after reflecting from the two surfaces. When two waves meet, they can add together, cancel each other, or partially cancel each other. This adding and canceling of light waves, called constructive interference and destructive interference, creates the rainbow-colored patterns that you see. White light is made up of all different colors mixed together. When light waves of a particular color meet and cancel each other, that color is subtracted from white light.