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. The thickness of the gap between the plates determines which colors of light cancel out at any one point. When a wave hits the top of the air layer, part reflects and part continues on. In addition, the wave that reflects from the bottom is inverted. Because the interference pattern depends on the amount of separation between the plates, what you're actually seeing is a topographical map of the distance between plates.