I'd always heard that archaeologists believed the ancient Greek and Roman monuments we know as serene, white marble were, originally, ridiculously RGB. Io9 has a great piece up explaining how researchers are able to definitively document the multicolored nature of classical art.
First, they scan the pieces with UV light, looking for fluorescent traces of organic pigments. Then, infrared and X-ray spectroscopy narrow down the chemical make-up of those pigments.
Spectroscopy relies on the fact that atoms are picky when it comes to what kind of incoming energy they absorb. Certain materials will only accept certain wavelengths of light. Everything else they reflect. Spectroscopes send out a variety of wavelengths, like scouts into a foreign land. Inevitably, a few of these scouts do not come back. By noting which wavelengths are absorbed, scientists can determine what materials the substance is made of. Infrared helps determine organic compounds. X-rays, because of their higher energy level, don't stop for anything less than the heavier elements, like rocks and minerals. Together, researchers can determine approximately what color a millennia-old statue was painted.
Via Irene Delse on Submitterator