Colour
colour (noun, pl. colours; American spelling: sl. color, pl. colors) – the subjective perception of an object caused by differential absorbance and reflection of light of different wavelengths and intensity. The way different colours are perceived by a visual apparatus like the human eye is intrinsically linked to three main attributes of colour: hue, chroma and lightness. The way colours can be reproduced depends on the device that is used for reproduction. Contrary to common belief, there are no absolute primary colours, i. e., there is no single set of colour hues that can produce all other hues. Instead, almost any three or more colours can be mixed to produce all other hues. The term primary colour is, nevertheless, commonly used to denote standard hues that generate colour on different devices. Colours can either be generated directly from light sources (e. g., television screens or computer monitors) or indirectly with inks that reflect or absorb light differently (e. g., printouts, photographs etc.). Mixing light of different hues results in an additive mixture, i. e., mixing hues of light that are opposite to one another on the colour wheel generates white (e. g., mixing yellow and blue light). Mixing ink of different hues results in a subtractive mixture, i. e., mixing hues of ink that are opposite to one another (e. g., yellow and blue) generates black (or, as a result of ink impurities: dark grey). Three colours, red (R), green (G), and blue (B), are typically used as primary additive colours to reproduce images from light sources. The three subtractive primary colours are cyan (C), magenta (M), and yellow (Y). These inks are typically used to reproduce colour from printouts. Inks suffer much more strongly from impurities than light. Thus, the gamut of colour (colour space) that can be reproduced with ink is typically much smaller than a gamut generated with light. To overcome some of these restrictions, printing devices therefore commonly utilize black (K) as a fourth subtractive "primary" colour.
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