Variable diffraction display

You’ve probably seen cars painted with ‘optically variable pigments’ (OVP). The colour of the car varies depending on the angle you look at it.

Optically variable pigments have millions of microscopic plates dispersed in a liquid. When the paint dries, the liquid evaporates off leaving layers of microscopic plates. Because the plates are all the same size and shape, collectively they act like a diffraction grating. Theoretically a single colour OVP is also possible (like a butterfly wing).

If the size/shape of the plates in a single colour OVP could be actively controlled, the colour of the paint could also be controlled. I propose the plates could be made of bi-metallic sheets. When the temperature changes the plates change shape, thus the average separation of plates changes, thus the colour changes. Of course this would only work if the plates remained dispersed in the liquid.

A display could be made using this technique. Each pixel would be a transparent well containing the pigment. The temperature of each pixel would be controlled with a small heating element.