Editing Yellow (section)

== Science and nature ==
=== Optics, color printing, and computer screens ===
{{infobox color
|title=Process Yellow (subtractive primary)
|hex=FFEF00
|source=[https://web.archive.org/web/20120626160106/http://www.tintbook.com/] [[CMYK]]
|isccname=Vivid greenish yellow
}}

<gallery mode="packed" heights="150">
File:CMYK color swatches.svg|Color printing typically uses ink of four colors: [[cyan]], [[magenta]], yellow, and [[Black|key]] (black). When CMY "primaries" are combined at full strength, the resulting "secondary" mixtures are red, green, and blue.
File:SubtractiveColor.svg|Mixing all three theoretically results in black, but imperfect ink formulations do not give true black, which is why an additional ''K'' component is needed.
File:NIEdot367.jpg|An example of color printing from 1902. Combining images in yellow, magenta and cyan creates a full-color picture.  This is called the CMYK color model.
File:Red and green make yellow.png|On a computer display, yellow is created by combining green and red light at the right intensity on a black screen.
</gallery>

Yellow is found between green and red on the spectrum of visible light. It is the color the human eye sees when it looks at light with a [[dominant wavelength]] between 570 and 590 nanometers.

In color printing, yellow is one of the three subtractive primary colors of ink along with [[magenta]] and [[cyan]]. Together with [[black]], they can be overlaid in the right combination to print any full color image. (See the [[CMYK color model]]).  A particular yellow is used, called Process yellow (also known as "pigment yellow", "printer's yellow", and "canary yellow"). Process yellow is not an RGB color, and there is no fixed conversion from CMYK primaries to RGB. Different formulations are used for printer's ink, so there can be variations in the printed color that is pure yellow ink.

The yellow on a color television or computer screen is created in a completely different way; by combining green and red light at the right level of intensity. (See [[RGB color model]]).

==== Complementary colors ====
{{See also|Complementary colors}}[[File:PlanckianLocusWithYellowComplements.png|thumb|upright|Complements of yellow have a dominant wavelength in the range 380 to 480&nbsp;nm. The green lines show several possible pairs of complementary colors with respect to different blackbody color temperature neutrals, illustrated by the "[[Planckian locus]]".]]
Traditionally, the complementary color of yellow is purple; the two colors are opposite each other on the color wheel long used by painters.<ref>{{cite book | last1 = Roelofs | first1 = Isabelle | last2 = Petillion | first2 = Fabien | title = La couleur expliquée aux artistes | year=2012 | publisher=Eyrolles | location=Paris | isbn=978-2-212-13486-5}}</ref> [[Vincent van Gogh]], an avid student of color theory, used combinations of yellow and purple in several of his paintings for the maximum contrast and harmony.<ref>{{cite book | first = John | last = Gage | year = 2006 | title = La Couleur dans l'art | pages = 50–51 }}</ref>

Hunt defines that "two colors are complementary when it is possible to reproduce the tristimulus values of a specified achromatic stimulus by an additive mixture of these two stimuli."<ref name=hunt>{{cite book | title = Measuring Color | first = J. W. G. | last = Hunt | year = 1980 | publisher = Ellis Horwood Ltd | isbn = 978-0-7458-0125-4}}</ref> That is, when two colored lights can be mixed to match a specified white (achromatic, non-colored) light, the colors of those two lights are [[Complementary color|complementary]]. This definition, however, does not constrain what version of white will be specified. In the nineteenth century, the scientists [[Hermann Grassmann|Grassmann]] and [[Hermann von Helmholtz|Helmholtz]] did experiments in which they concluded that finding a good complement for spectral yellow was difficult, but that the result was indigo, that is, a wavelength that today's color scientists would call violet or purple. Helmholtz says "Yellow and indigo blue" are complements.<ref>{{cite book | title = Physiological Optics | first = Hermann | last = von Helmholtz | publisher = Dover | year = 1924 | isbn = 978-0-486-44260-0}}</ref> Grassmann reconstructs Newton's category boundaries in terms of wavelengths and says "This indigo therefore falls within the limits of color between which, according to Helmholtz, the complementary colors of yellow lie."<ref>{{cite journal | title = Theory of Compound Colors | first = Hermann Günter | last = Grassmann | journal = Philosophical Magazine | volume =4 | year = 1854 | pages = 254–64 }}</ref>

Newton's own color circle has yellow directly opposite the boundary between indigo and violet. These results, that the complement of yellow is a wavelength shorter than 450&nbsp;nm, are derivable from the modern [[CIE 1931]] system of colorimetry if it is assumed that the yellow is about 580&nbsp;nm or shorter wavelength, and the specified white is the color of a blackbody radiator of temperature 2800 [[kelvin|K]] or lower (that is, the white of an ordinary incandescent light bulb). More typically, with a daylight-colored or around 5000 to 6000 K white, the complement of yellow will be in the blue wavelength range, which is the standard modern answer for the complement of yellow.

Because of the characteristics of paint pigments and use of different [[color wheel]]s, painters traditionally regard the complement of yellow as the color indigo or blue-violet.

==== Lasers ====
[[Laser]]s emitting in the yellow part of the spectrum are less common and more expensive than most other colors.<ref name="laserglow">{{cite web |url=http://www.laserglow.com/index.php?portable |title=Laserglow – Blue, Red, Yellow, Green Lasers |publisher=Laserglow.com |access-date=27 March 2009 |quote=described as an "extremely rare yellow". |archive-date=24 March 2009 |archive-url=https://web.archive.org/web/20090324123802/http://www.laserglow.com/index.php?portable |url-status=live }}</ref> In commercial products diode pumped solid state ([[Diode-pumped solid-state laser|DPSS]]) technology is employed to create the yellow light. An infrared laser diode at 808&nbsp;nm is used to pump a crystal of neodymium-doped yttrium vanadium oxide (Nd:YVO4) or neodymium-doped yttrium aluminum garnet (Nd:YAG) and induces it to emit at two frequencies (281.76&nbsp;THz and 223.39&nbsp;THz: 1064&nbsp;nm and 1342&nbsp;nm wavelengths) simultaneously. This deeper infrared light is then passed through another crystal containing potassium, titanium and phosphorus (KTP), whose non-linear properties generate light at a frequency that is the sum of the two incident beams (505.15&nbsp;THz); in this case corresponding to the wavelength of 593.5&nbsp;nm ("yellow").<ref name="ledmuseum">{{cite web |url=http://ledmuseum.candlepower.us/yelldpss.htm |title=Yellow (593.5&nbsp;nm) DPSS Laser Module |last=Johnson |first=Craig |date=22 March 2009 |publisher=The LED Museum |access-date=27 March 2009 |archive-date=16 February 2009 |archive-url=https://web.archive.org/web/20090216143902/http://ledmuseum.candlepower.us/yelldpss.htm |url-status=live }}</ref> This wavelength is also available, though even more rarely, from a [[helium–neon laser]]. However, this not a true yellow, as it exceeds 590&nbsp;nm. A variant of this same DPSS technology using slightly different starting frequencies was made available in 2010, producing a wavelength of 589&nbsp;nm, which is considered a true yellow color.<ref name="laserglow2">{{cite web |url=http://www.laserglow.com/GRH |title=Laserglow – Blue, Red, Yellow, Green Lasers |publisher=Laserglow.com |access-date=12 August 2011 |archive-date=5 August 2011 |archive-url=https://web.archive.org/web/20110805054301/https://www.laserglow.com/GRH |url-status=live }}</ref> The use of yellow lasers at 589&nbsp;nm and 594&nbsp;nm have recently become more widespread thanks to the field of [[optogenetics]].<ref name="laserglow3">{{cite web |url=http://www.laserglow.com/page/optogenetics |title=Laserglow – Blue, Red, Yellow, Green Lasers |publisher=Laserglow.com |access-date=20 September 2011 |archive-date=15 September 2011 |archive-url=https://web.archive.org/web/20110915023159/http://www.laserglow.com/page/optogenetics |url-status=live }}</ref>

=== Astronomy ===
{{See also|Astronomy|Yellow supergiant|Cepheid variable}}

[[Star]]s of [[Stellar classification|spectral class]]es F and G have [[color temperature]]s that make them look "yellowish".<ref>{{cite book
| title = Stars and Galaxies
| first = Ron
| last = Miller
| publisher = Twenty-First Century Books
| year = 2005
| isbn = 978-0-7613-3466-8
| page = 22
| url = https://books.google.com/books?id=QL9uAfad1ggC&q=spectral-class+yellow&pg=PA22
| access-date = 23 November 2020
| archive-date = 20 March 2023
| archive-url = https://web.archive.org/web/20230320151550/https://books.google.com/books?id=QL9uAfad1ggC&q=spectral-class+yellow&pg=PA22
| url-status = live
}}</ref> The first astronomer to classify stars according to their color was [[Friedrich Georg Wilhelm von Struve|F. G. W. Struve]] in 1827. One of his classifications was {{lang|la|flavae}}, or yellow, and this roughly corresponded to stars in the modern spectral range F5 to K0.<ref>{{cite book | first=Paul | last=Murdin | year=1984 | page=[https://archive.org/details/coloursofstars0000mali/page/18 18] | title=Colours of the stars | publisher=CUP Archive | isbn=978-0-521-25714-5 | url=https://archive.org/details/coloursofstars0000mali/page/18 }}</ref> The [[Strömgren photometric system]] for stellar classification includes a 'y' or yellow filter that is centered at a wavelength of 550&nbsp;nm and has a bandwidth of 20–30&nbsp;nm.<ref>{{cite journal
| last=Strömgren | first=Bengt
| title=Main Sequence Stars, Problems of Internal Constitution and Kinematics (George Darwin Lecture)
| journal=Quarterly Journal of the Royal Astronomical Society | volume=8 | pages=8–37 | bibcode=1963QJRAS...4....8S
| year=1963
}}</ref><ref>{{Cite book
| last1 = Norton | first1 = Andrew | last2 = Cooper | first2 = W. Alan
| title=Observing the universe: a guide to observational astronomy and planetary science
| year=2004
| isbn=978-0-521-60393-5 | page=63 | publisher = Cambridge University Press | bibcode = 2004ougo.book.....N }}</ref>

[[Supergiant]] stars are rarely [[Yellow supergiant|yellow supergiants]] because F and G class supergiants are physically unstable; they are most often a transitional phase between [[blue supergiants]] and [[Red supergiant|red supergiants]]. Some yellow supergiants, the [[Cepheid variables]], pulsate with a period proportional to their [[absolute magnitude]]; hence, if their [[apparent magnitude]] is known, the distance to them can be calculated with great precision.<ref>{{Cite journal |last=Parsons |first=S. B. |date=1971-04-01 |title=Effective Temperatures, Intrinsic Colours, and Surface Gravities of Yellow Supergiants and Cepheids |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=152 |issue=1 |pages=121–131 |doi=10.1093/mnras/152.1.121 |doi-access=free |issn=0035-8711}}</ref> Cepheid variables were hence used to determine distances within and beyond the [[Milky Way]] galaxy. The most famous example is the current North Pole star, [[Polaris]].

=== Biology ===
Autumn [[leaves]], yellow flowers, bananas, oranges and other yellow fruits all contain [[carotenoid]]s, yellow and red organic pigments that are found in the [[chloroplast]]s and [[chromoplast]]s of plants and some other [[photosynthetic]] organisms like [[algae]], some bacteria and some fungi. They serve two key roles in plants and algae: they absorb light energy for use in [[photosynthesis]], and they protect the green [[chlorophyll]] from photodamage.<ref name="fasebj.org"/>

In late summer, as [[daylight]] hours shorten and temperatures cool, the [[vein]]s that carry fluids into and out of the leaf are gradually closed off. The water and mineral intake into the leaf is reduced, slowly at first, and then more rapidly. It is during this time that the chlorophyll begins to decrease. 
As the chlorophyll diminishes, the yellow and red carotenoids become more and more visible, creating the classic [[autumn leaf color]].

Carotenoids are common in many living things; they give the characteristic color to carrots, maize, [[daffodil]]s, [[rutabaga]]s, [[buttercup]]s and bananas. They are responsible for the red of cooked [[lobster]]s, the pink of [[flamingoes]] and [[salmon]] and the yellow of [[Domestic canary|canaries]] and [[egg yolk]]s.

[[Xanthophylls]] are the most common yellow [[pigment]]s that form one of two major divisions of the carotenoid group. The name is from Greek ''xanthos'' ({{lang|grc|ξανθος}}, "yellow") + ''phyllon'' ({{lang|grc|φύλλον}}, "leaf"). Xanthophylls are most commonly found in the leaves of green plants, but they also find their way into animals through the food they eat. For example, the yellow color of chicken egg yolks, fat, and skin comes from the feed the chickens consume. Chicken farmers understand this, and often add [[xanthophyll]]s, usually [[lutein]], to make the egg yolks more yellow.

Bananas are green when they are picked because of the chlorophyll their skin contains. Once picked, they begin to ripen; [[hormones]] in the bananas convert amino acids into ethylene gas, which stimulates the production of several [[enzymes]]. These enzymes start to change the color, texture and flavor of the banana. The green chlorophyll supply is stopped and the yellow color of the carotenoids replaces it; eventually, as the enzymes continue their work, the cell walls break down and the bananas turn brown.

<gallery mode="packed" heights="140px">
File:Fall colors near the Eagle Lake trailhead.jpg|Autumn colors along the [[Eagle River (Cook Inlet)|Eagle River]] near [[Anchorage]], [[Alaska]]
File:Cornwall Daffodils.jpg|[[Daffodils]] in Cornwall
File:Bananas.jpg|[[Banana]]s, like autumn [[leaves]], [[Domestic canary|canaries]] and [[egg yolks]], get their yellow color from natural pigments called [[carotenoids]].
File:Raw egg.jpg|The yolk of a raw egg. The color comes from the [[xanthophyll]] carotenoids [[lutein]] and [[zeaxanthin]]
File:Duckling chicks (Unsplash).jpg|Duckling chicks
</gallery>

==== Fish ====
* [[Yellowtail (fish)|Yellowtail]] is the common name for dozens of different fish species that have yellow tails or a yellow body. Most of the time, yellowtail (fish) actually refers to Japanese amberjack, a fish that lives between Japan and Hawaii.
* [[Yellowfin tuna]] (''Thunnus albacares'') is a species of tuna, having bright yellow [[Anal fin|anal]] and second [[dorsal fin]]s. Found in tropical and subtropical seas and weighing up to {{convert|200|kg|lb|abbr=on}}, it is caught as a replacement for depleted stocks of [[bluefin tuna]].
* [[Smallmouth yellowfish]] (Labeobarbus aeneus) is a species of [[ray-finned fish]] in the genus [[Labeobarbus]]. It has become an invasive species in rivers of the Eastern Cape, South Africa, such as the Mbhashe River.

==== Insects ====
[[File:European wasp white bg.jpg|thumb|A [[yellow jacket]] [[wasp]]]]
* The [[yellow-fever mosquito]] (''Aedes aegypti'') is a mosquito so named because it transmits [[dengue fever]] and [[yellow fever]], the mosquito-borne viruses.
* [[Yellowjacket]]s are black-and-yellow [[wasp]]s of the genus ''Vespula'' or ''Dolichovespula'' (though some can be black-and-white, the most notable of these being the [[bald-faced hornet]], ''Dolichovespula maculata''). They can be identified by their distinctive black-and-yellow color, small size (slightly larger than a [[bee]]), and entirely black [[Antenna (biology)|antennae]].

==== Trees ====
[[File:Snowbowlaspens.jpg|thumb|left|American aspens, ''[[Populus tremuloides]]'']]
* [[Populus tremuloides]] is a [[deciduous]] tree native to cooler areas of North America, one of several species referred to by the common name [[aspen]].  ''Populus tremuloides'' is the most widely distributed tree in North America, being found from Canada to central Mexico.
* The [[yellow birch]] (''Betula alleghaniensis'') is a [[birch]] species native to eastern North America, from [[Nova Scotia]], [[New Brunswick]], and southern [[Quebec]] west to [[Minnesota]], and south in the Appalachian Mountains to northern Georgia. They are medium-sized [[deciduous]] trees and can reach about {{convert|20|m|abbr=on}} tall, trunks up to {{convert|80|cm|abbr=on}} in diameter. The bark is smooth and yellow-bronze,<ref>{{cite web|url=http://landscaping.about.com/cs/fallfoliagetrees/a/fall_foliage4.htm|archive-url=https://web.archive.org/web/20040105225057/http://landscaping.about.com/cs/fallfoliagetrees/a/fall_foliage4.htm|url-status=dead|archive-date=5 January 2004|title=Fall Foliage of 4 Types of Birch Trees|first=David|last=Beaulieu|website=About.com Home}}</ref> and the wood is extensively used for flooring, cabinetry, and toothpicks.
* The [[Thorny Yellowwood]] is an Australian rainforest tree which are valued for their deep yellow-white wood.
* [[Liriodendron|Yellow poplar]] is a common name for ''[[Liriodendron]]'', the [[tuliptree]]. The common name is inaccurate as this genus is not related to poplars.
* The ''[[Handroanthus albus]]'' is an urban tree with yellow flowers native to the [[Cerrado]] of Brazil.