Colour spaces. Comparison between the achievable colours (or colour spaces) in subtractive and additive colour systems. Subtractive colour is used in printing, and has the acronym CMYK. Cyan, magenta and yellow dyes selectively filter out the incident light to present the impression of colour while a black channel (K) is used to enrichen dark colours. Additive colour is used in TV, video and computer screens and projection equipment. Also called RGB colour, it uses various proportions of red, green and blue light mixed together to provide the colour impression. Note that the RGB space encompasses denser and richer colours than the CMYK space, especially in greens and cyans.