Coins shown in false color. Source
We are all used to the rich yellow of gold and the cool shine of silver, but new research says that we can change the colors of metals like this without staining them with dye or covering them with a pigment. How? The answer is nanotechnology. The colors that we perceive are just different wavelengths of light, so it is possible to create structures on a small scale to interfere with these wavelengths. The idea is that we could create certain patterns on the nanometer scale to alter which wavelengths are absorbed and which wavelengths are reflected.
To read more, check out this article.