Editing Ewald Hering (section)

===Color theory===

Hering disagreed with the leading theory developed primarily by [[Thomas Young (scientist)|Thomas Young]], [[James Clerk Maxwell]] and [[Hermann von Helmholtz]].<ref name="Turner, R. M.-1994">{{cite book |author=Turner, R. M. |title=In the eye's mind: vision and the Helmholtz-Hering controversy |publisher=Princeton University Press |location=Princeton, N.J |year=1994 |isbn=978-0-691-03397-6 }}</ref> 
Young proposed that color vision is based on three [[primary color]]s: red, green, and blue. Maxwell demonstrated that any color can be matched by a mixture of three primary colors. This was interpreted by Helmholtz as proof that humans perceive colors through three types of receptors, while white and black would reflect the amount of light.

Hering instead held that the visual system works based on a system of [[Opponent process|color opponency]]. His evidence stemmed from color-adaptation experiments and the linguistic observation that certain color names cannot be combined into one. In this model, colors are perceived through mechanisms sensitive to three pairs of opponent colors: red-green, yellow-blue and white-black.

[[Johannes von Kries]] published in 1905 the ''[[zone theory]]'' that synthesizes both descriptions as one, where the Young-Helmholtz theory describes the interaction of light with receptors and Hering the image processing stage.<ref name="Moore-1992">{{Citation|url=https://books.google.com/books?id=m-YF1glKWLoC&pg=PA128|last=Moore|first=Walter John|title=Schrödinger: Life and Thought|isbn=9780521437677|date=29 May 1992|publisher=Cambridge University Press }}</ref>
Later, in 1925, [[Erwin Schrödinger]] published a paper inspired by von Kries, titled ''On the relation of the four color to the three color theory''. There he probes a formal relationship between the two color theories.<ref name="Moore-1992"/>

Both theories have solid empirical evidence. The conundrum was resolved by the discovery of color-opponent ganglion cells in the [[retina]] and [[lateral geniculate nucleus]]. We now know that the human eye possesses three types of color-sensitive receptors (as proposed by Young, Maxwell, and Helmholtz) which then combine their signals in three color-opponent channels as proposed by Hering. Thus, both the Hering and Young-Helmholtz theories are correct.{{dubious|date=February 2025}}