Gray (hue / variety / modifier): Abbreviated (GY). A perceived colour hue resembling the colour of the metal nickel, aluminum, or pewter. Gray is a neutral colour containing little or no saturation (i.e. , an achromatic hue). Gray is a “nonspectral” colour that may be produced by mixing black and white in varying proportions. 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. Gray colours often appear very different when viewed under average natural daylight (6500 K) versus other artificial (tungsten or fluorescent) light sources. For example, a neutral gray that appears pure gray in daylight may appear warmer (yellowish gray) when viewed under an incandescent lamp or cooler (bluish gray) under a fluorescent lamp (see Colour rendition). In the diamond trade, gray (GY) represents one of the basic twelve colour varieties. Gray diamonds can also contain secondary modifiers such as blackish gray (bk-GY), bluish gray (b -GY), brownish gray (br-GY), greenish gray (g -GY), olivish gray (ol -GY), pinkish gray (pk-GY), purplish gray (pp-GY), violetish gray (v-GY), whitish gray (wh-GY), and yellowish gray (y-GY). Gray can also occur as a secondary colour modifier in other colour varieties such as grayish yellow (gy-Y), gray-blue (GY-B), etc. Natural gray diamonds occur within a specific region of colour tone. Their lightness extends from very light (smoke) gray, light (nickel) gray, medium (pewter) gray through dark (graphite) gray colours, while saturation is confined to the weak range. Popular names for different mixtures of gray are: aluminum, ash, cadet, charcoal, dove, flint, graphite, gull, gun metal, lead, mouse, nickel, oyster, pearl , pewter, pigeon, plumbago, shadow, silver, slate, smoke, steel, and taupe