Diamond possesses many qualities, which make it an ideal gemstone. It is extremely hard, and also very tough and hard wearing, and this also helps it to take a very high polish. Some hard articles are brittle which detracts from their durability. There are some things, which are harder than diamond. In its pure form it is colorless, has a high refractive index, so has a very high luster. It possesses high dispersion, meaning that different light wavelengths are diffracted differently, giving a strong scintillating play of prismatic colors.
Pure diamond, if such a thing exists, is colorless. Most diamonds are slightly colored, even if the coloring is almost imperceptible. The commonest color is yellow, which is caused by tiny amounts of nitrogen being present in the crystal structure; others are gray, light brown or greenish. Diamond can be almost any color, although strongly colored attractive specimens are very rare, and as such are not actively promoted. Probably in case consumers realize that blue, red, green and other colors are attractive, and start buying sapphires, rubies, emeralds and other gemstones instead of diamonds!
As with many gemstones, colors can be artificially produced or modified.
Colored diamonds in trade go under the name “fancy color”. Because of their rarity they are held in very esteem, especially when the color displays an intense saturation. The most valuable diamond, however are the completely colorless stones- in this respect diamond is the only gemstone whose colorlessness renders it more valuable.