Diamonds with Gray as the primary dominant colour are unique. These diamonds are comparatively reasonably priced and have a perceived colour resembling the colour of the metal nickel, aluminium, or pewter.
Gray is a neutral colour containing little or no saturation. The addition of small quantities of blue or green will produce a cool gray colour, while the addition of brown or yellow will produce a warm gray colour. Common names for gray colour diamonds include 
charcoal gray, steel, pigeon, slate, silver etc. The gray diamond rough is mined in Australia, South Africa, India, Russia and Brazil. Gray diamonds are coloured by hydrogen, and more rarely boron (unknown how, since boron nearly always forms blue). The defect causes the stone to absorb all wavelengths of light equally. Gray colour can tint nearly every other shade. Gray colours often appear very different when viewed under average natural daylight versus an artificial light source. Natural gray diamonds occur within a specific region of colour tone. Their lightness extends from very light (smoke) gray, through dark (graphite) gray colours.
