Grey or gray is an intermediate color between black and white, a neutral or achromatic color, meaning literally a color "without color."  It is the color of a cloud-covered sky, of ash and of lead.
The first recorded use of grey as a color name in the English language was in AD 700. Grey is the British, Canadian, Australian, Irish, New Zealand and South African spelling, although gray remained in common usage in the UK until the second half of the 20th century. Gray is the preferred American spelling since approximately 1825,, although grey is an accepted variant
In color theory, colors are represented and produced by several models. In computer technology (display terminals) and entertainment system displays (television sets) color is represented in theRGB color model. The name derives as an acronym for the colors red, green, and blue. Any color is represented by a mixture in varying intensities of red, green, and blue. To produce grey in RGB displays, red, green, and blue primary light sources are combined in proportions equal to that of the white point.
In printing and graphic design the CMYK color model is often preferred. It is a four-color process, using the primary colors cyan, magenta, yellow, and black (key). Grey is produced either by the black channel, or by an approximately equal combination of C, M, and Y primary colors. Images consisting wholly of neutral colors are called monochrome, black-and-white or greyscale.
Two colors are called complementary colors if grey is produced when they are combined additively or subtractively. Grey is its own complement. Many color models place complements opposite each other in a color wheel.
Most grey pigments have a cool or warm cast to them, as the human eye can detect even a minute amount of saturation. Yellow, orange, and red create a "warm grey". Green, blue, and violet create a "cool grey". When there is no cast at all, it is referred to as "neutral grey",