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This system is in effect a simplified version of Newton's geometrical rule that colours closer together on the hue circle will produce more vibrant mixtures. A mixture produced from two primary colours, however, will be much more highly saturated than one produced from two secondary colours, even though the pairs are the same distance apart on the hue circle, revealing the limitations of the circular model in the prediction of colour-mixing results. For example, a mixture of magenta and cyan inks or paints will produce vivid blues and violets, whereas a mixture of red and blue inks or paints will produce darkened violets and purples, even though the angular distance separating magenta and cyan is the same as that separating red and blue.
== ColorColour contrast ==
{{See also|colorcolour contrast}}
In [[Michel Eugène Chevreul]]'s 1839 book ''The principles of harmony and contrast of colours'',<ref name=Chevreul>{{cite book |last1=Chevreul |first1=Michel Eugène |title=De la loi du contraste simultané des couleurs |date=1839}}</ref> he introduced the law of colorcolour contrast, stating that colorscolours that appear together (spatially or temporally) will be altered as if mixed with the complementary colorcolour of the other colorcolour, functionally boosting the colorcolour contrast between them. For example, a piece of yellow fabric placed on a blue background will appear tinted orange because orange is the complementary colorcolour to blue. Chevreul formalizedformalised three types of contrast:<ref name=Chevreul/>
* ''simultaneous contrast'', which appears in two colorscolours viewed side by side
* ''successive contrast'', for the [[afterimage]] left on an achromatic background after viewing a colorcolour
* ''mixed contrast'', for the afterimage left on another colorcolour
=== Warm vs. cool colorscolours <span class="anchor" id="Warm vs. cool colours"></span>===
The distinction between "warm" and "cool" colorscolours has been important since at least the late 18th century.<ref>{{cite web|url=http://www.handprint.com/HP/WCL/color12.html |title=color temperature |publisher=handprint |date=2009-04-19 |access-date=2011-06-09}}</ref> The difference (as traced by etymologies in the [[Oxford English Dictionary|''Oxford English Dictionary'']]), seems related to the observed contrast in landscape light, between the "warm" colorscolours associated with daylight or sunset, and the "cool" colorscolours associated with a graygrey or overcast day. Warm colorscolours are often said to be hues from red through yellow, browns, and tans included; cool colorscolours are often said to be the hues from blue-green through blue violet, most graysgreys included. There is a historical disagreement about the colorscolours that anchor the polarity, but 19th-century sources put the peak contrast between red-orange and greenish-blue.{{NoteTag|The traditional warm/cool association of a colorcolour is reversed relative to the [[colorcolour temperature]] of a theoretical radiating [[black body]]; the hottest [[star]]s radiate blue (cool) light, and the coolest radiate red (warm) light.}}
ColorColour theory has described perceptual and psychological effects to this contrast. Warm colorscolours are said to advance or appear more active in a painting, while cool colorscolours tend to recede; used in interior design or fashion, warm colorscolours are said to arouse or stimulate the viewer, while cool colorscolours calm and relax.<ref>{{Cite journal|last=Singh|first=Satyendra|date=2006-01-01|title=Impact of colorcolour on marketing|url=https://doi.org/10.1108/00251740610673332|journal=Management Decision|volume=44|issue=6|pages=783–789|doi=10.1108/00251740610673332|issn=0025-1747|url-access=subscription}}</ref> Most of these effects, to the extent they are real, can be attributed to the higher saturation and lighter value of warm pigments in contrast to cool pigments; brown is a dark, unsaturated warm colorcolour that few people think of as visually active or psychologically arousing.
== Color harmony and color schemes ==
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