Editing Primary color (section)

== Psychological primaries ==
[[File:Hering Color Cricles.png|thumb|upright=1.0|[[Ewald Hering]]'s illustration<ref>{{cite book |last1=Hering |first1=Ewald |title=Grundzüge der Lehre vom Lichtsinn |year=1920 |publisher=Springer Berlin Heidelberg |isbn=978-3-662-42174-1 |url=https://books.google.com/books?id=M1xVAAAAMAAJ |language=de}}</ref> of the psychological primaries. Red/green and yellow/blue form opponent pairs (top). Each color can be psychologically mixed to make other colors (bottom) with both members of the other pair but not with its opponent according to Hering.]]
{{Main|Unique hues}}

The [[opponent process]] was proposed by [[Ewald Hering]] in which he described the four [[unique hues]] (later called psychological primaries in some contexts): red, green, yellow and blue.<ref>{{cite book |last1=Hering |first1=Ewald |title=Outlines of a theory of the light sense. |date=1964 |publisher=Harvard Univ. Press |language=English}}</ref> To Hering, the unique hues appeared as pure colors, while all others were "psychological mixes" of two of them. Furthermore, these colors were organized in "opponent" pairs, red vs. green and yellow vs. blue so that mixing could occur across pairs (e.g., a yellowish green or a yellowish red) but not within a pair (i.e., [[reddish green]] cannot be imagined). An achromatic opponent process along black and white is also part of Hering's explanation of color perception. Hering asserted that we did not know why these color relationships were true but knew that they were.<ref>{{cite book |last1=Turner |first1=R. Steven |title=In the eye's mind : vision and the Helmholtz-Hering controversy |date=1994 |publisher=Princeton University Press |location=Princeton, New Jersey |isbn=9781400863815 |pages=130–133 |language=en}}</ref> Although there is a great deal of evidence for the opponent process in the form of neural mechanisms,<ref>{{cite journal
| last1   = Conway
| first1  = Bevil R.
| title   = Color Vision, Cones, and Color-Coding in the Cortex
| journal = The Neuroscientist
| date    = 12 May 2009
| volume  = 15
| issue   = 3
| pages   = 274–290
| doi     = 10.1177/1073858408331369
| pmid = 19436076
| s2cid = 9873100
}}</ref> there is currently no clear mapping of the psychological primaries to [[neural correlate]]s.<ref>{{cite book |last1=MacLeod |first1=Donald |editor1-last=Cohen |editor1-first=Jonathan |editor2-last=Matthen |editor2-first=Mohan |title=Color Ontology and Color Science |date=21 May 2010 |publisher=MIT Press |isbn=978-0-262-01385-7 |pages=159–162 |url=https://books.google.com/books?id=-SYTDgAAQBAJ&q=Into+the+Neural+Maze.+In%3A+Color+Ontology+and+Color+Science.&pg=PA151 |language=en|quote="Many color scientists, acknowledging that the color opponent signals observed in the pathway to cortex have no relation to the psychological primaries, do nevertheless take it for granted that a color opponent neural representation capable of accounting for the phenomenally simple or unitary quality of the psychological primaries must exist somewhere in the brain—in a region that is directly reflected in phenomenal experience, instead of merely conveying signals from the eye. This tenet was long maintained in the absence of neurophysiological evidence, and continues to be maintained even though current neurophysiological evidence does not support it."}}</ref>

The psychological primaries were applied by [[Richard S. Hunter]] as the primaries for [[Hunter Lab|Hunter L,a,b]] colorspace that led to the creation of [[CIELAB color space|CIELAB]].<ref>{{cite web |title=Application Note AN 1005.00 Measuring color using Hunter L, a, b versus CIE 1976 L*a*b* |url=https://www.hunterlab.com/media/documents/duplicate-of-an-1005-hunterlab-vs-cie-lab.pdf |archive-url=https://web.archive.org/web/20210829054654/https://www.hunterlab.com/media/documents/duplicate-of-an-1005-hunterlab-vs-cie-lab.pdf |archive-date=2021-08-29 |url-status=live |website=HunterLab |publisher=Hunter Associates Laboratory Inc |access-date=10 March 2021 |quote=Hunter L, a, b and CIE 1976 L*a*b* (CIELAB) are both color scales based on the Opponent-Color Theory.}}</ref> The [[Natural Color System]] is also directly inspired by the psychological primaries.<ref>{{cite book
| last1     = Maffi
| first1    = Luisa
| editor-last1 = Hardin
| editor-first1 = C.L.
| title     = Color categories in thought and language
| date      = 1997
| publisher = Cambridge University Press
| location  = Cambridge
| isbn      = 978-0-521-49800-5
| pages     = 163–192
| edition   = 1. publ.
| url       = https://books.google.com/books?id=ix8l5X5ZBogC&q=%22natural+color+system%22&pg=PA163
}}</ref>