Within arm's length of me are multiple examples of reflective displays that conserve power by operating without a backlight. One of the displays is actually a writing tablet that utilizes liquid crystals while the others are eink readers that move small particles to create images. While largely the technologies are different, both technologies monochromatic, but researchers at the University of Michigan are looking to change that.
Iridescence is a phenomenon that is not uncommon in Nature, as it is what gives peacock feathers' their color, amongst other materials. The various colors of a peacock feather are created by special grooves that only reflect certain colors of light, but the angle you view the grooves at affects the color you see. The researchers have successfully replicated the iridescent effect without that angle dependency by etching nanoscale cavities into a surface. When light falls on these cavities, a specific frequency is trapped, so it is missing from what is reflected back to your eyes. (The etching holds the negative of the image you see.)
So far the researchers have only produced static images this way, but they hope to create moving images this way soon. When that is achieved, it will be interesting to see what uses the technology will have, as displays and counterfeit-protection already come to mind.
Source: University of Michigan