Researchers have figured out how to use a specific engraving technique in order to alter the frequency of light a metal—any metal—absorbs or reflects. How? By carving tiny rings, smaller than the wavelengths of light.
Gold normally absorbs blue light, which gives it its yellowish hue. Silver metals absorb and emit just about every frequency of visible of light (which means... they're actually colorless).
By carving a pattern of rings onto a metal's surface, the properties of its electrons, called the resonant frequency, is altered. By varying the size and depth of these rings, the frequency of light a metal absorbs and reflects is changed. No other properties of the metal are affected.
This is essentially the same technique that scientists are using to create invisibility cloaks, except that instead of trying to make light pass through a material, they just want to redirect how light is reflected and absorbed. [Technology Review]