Crossed polarized filters showing stress patterns in plastic.
It looks like what you see when you look through a polariscope, a device which reveals things like stress patterns in glasses and plastics, among other things. It works by interposing the object to be studied between two polarizers, which are oriented such that their planes of polarization are perpendicular. Variations in the rotation of polarization in the object reveal themselves as changing colors.
The patterns actually appear to be the result of multiple overlapping pieces of self-adhesive tape - there’s an exhibit like this in childrens’ are of the science museum in London.
Behind the plastic sheet there is a polarized light* shining on it. The sheet has random strips of plastic/tape stuck on it. Many plastics rotate the plane of polarization of light that passes thru them. (The direction of rotation is related to the direction of rotation of the polymer chains in the plastics.) The amount of rotation is dependent on the material, the thickness and the wavelength of light.
The viewer is holding up a piece of polarized plastic. If the combination of rotations effects are just right, light will pass thru, else it is blocked. So if a particular area rotates red light the right amount you see red, etc.
Q.E.D.: the polarized plastics sheets in a polarizer can be at right angles. The are rotatable so that by adjusting them you can enhance the contrast of rotation. In some cases, you might want their planes of polarization in parallel to get maximum effect.
*You can actually use unpolarized light, esp. if it shines at a nice “Brewster’s angle”.