Grey on televisions, computer displays and telephones is usually created using the RGB color model. Red, green, and blue light combined at full intensity on the black screen makes white; by lowering the intensity, it is possible to create different shades of grey. In printing, grey is usually obtained with the CMYK color model, using cyan, magenta, yellow and black. Grey is produced either by using black and white, or by combining equal amounts of cyan, magenta and yellow. Most greys have a cool or warm cast to them, as the human eye can detect even a minute amount of color
Secondary color secondary CMY colors (with secondary colors in boldface) are: Ideally, combining three perfect primary colors in equal amounts would produce black, but this is impossible to achieve in practice. Therefore a "key" pigment, usually black, is added to printing to produce dark shades more efficiently. This combination is referred to as CMYK, where K stands for Key. Before the discovery of CMY, at least as far back as Goethe, the best primary colors were thought to be red, yellow, and blue. Mixing these pigments in equal amounts produces orange, green, and purple: That is, the primary and secondary RYB colors