Editing Eye color (section)

==Eye color range==
As is the case with [[hair color]] and [[skin color]], the melanin that is usually produced in the bodies of almost all mammals is either [[eumelanin]] or [[pheomelanin]], resulting in a high proportion of black, brown, red, and yellow coloring in the biological features that make use of it. As such, most mammals generally have a predominantly orange-based color palette, which generally varies from light orange colors like [[Peach (color)|peach]] to dark orange colors like [[brown]]; sometimes even more varied colors like [[maroon]] are exhibited.

===Brown===
{{Redirect|Brown eyes}}
[[File:MyStrangeIris.JPG|thumb|A brown iris]]
Almost all mammals have brown or darkly-pigmented irises.<ref>Brenda J Bradley, Anja Pedersen, Nicholas I Mundy: [https://pubmed.ncbi.nlm.nih.gov/19278018/ Blue eyes in lemurs and humans: same phenotype, different genetic mechanism]  Am J Phys Anthropol. 2009</ref> In humans, brown is by far the most common eye color, with approximately 79% of people in the world having it.<ref name=":0">{{Cite web|last=Debrowski|first=Adam|title=Which Eye Colors Are the Rarest?|url=https://www.allaboutvision.com/eye-anatomy/rarest-eye-color/|access-date=2021-02-04|website=All About Vision|language=en-us}}</ref> Brown eyes result from a relatively high concentration of melanin in the stroma of the iris, which causes light of both shorter and longer wavelengths to be absorbed.<ref name="Fox">{{cite book |last=Fox |first=Denis Llewellyn |title=Biochromy: Natural Coloration of Living Things |publisher=University of California Press |year=1979 |page=9 |url=https://books.google.com/books?id=c2xyxwlm2UkC&pg=PA9|isbn=978-0-520-03699-4}}</ref>

[[File:Human_eye,_anterior_view.jpg|right|thumb|A light brown iris with limbal ring]]

In many parts of the world, it is nearly the only iris color present.<ref>{{OMIM|227220|SKIN/HAIR/EYE PIGMENTATION, VARIATION IN, 1; SHEP1}}</ref> Brown eyes are common in [[Europe]], [[East Asia]], [[Southeast Asia]], [[Central Asia]], [[South Asia]], [[West Asia]], [[Oceania]], [[West Africa]] and the [[Americas]].<ref name="Sulem"/> Light or medium-pigmented brown eyes can also be commonly found in [[Europe]], among the [[Americas]], and parts of [[Central Asia]], [[West Asia]], [[South Asia]], and [[East Africa]]. Light brown eyes bordering amber and hazel coloration are more common in [[Europe]], but can also be observed in [[East Asia]], [[Southeast Asia]], [[North Africa]] and [[East Africa]].
<!--- [[File:225 of 'The Races of Great Britain. A contribution to the anthropology of Western Europe. (With plates and maps.)' (11176801375).jpg|thumb|189x240px|Percentage of dark eyes among British military recruits in the 19th century by region]] --->
===Amber===
[[File:Ambereye.jpg|thumb|Amber eye]]
Amber eyes are a solid color with a strong yellowish/golden or russet/coppery tint, which may be due to a yellow pigment called [[lipochrome]]  (also found in green eyes).<ref>[http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html Howard Hughes Medical Institute: Ask A Scientist] {{webarchive|url=https://web.archive.org/web/20100901150309/http://www.hhmi.org/cgi-bin/askascientist/highlight.pl?kw=&file=answers%2Fgenetics%2Fans_044.html |date=1 September 2010 }}. Hhmi.org. Retrieved on 23 December 2011.</ref><ref>Larry Bickford [http://www.eyecarecontacts.com/eyecolor.html Eye Color] {{webarchive|url=https://web.archive.org/web/20101023191830/http://www.eyecarecontacts.com/eyecolor.html |date=23 October 2010 }}. Eyecarecontacts.com. Retrieved on 23 December 2011.</ref> Amber eyes should not be confused with hazel eyes. Although hazel eyes may contain specks of amber or gold, they usually tend to have many other colors, including green, brown, and orange. Also, hazel eyes may appear to shift in color and consist of flecks and ripples, while amber eyes are of a solid gold hue. Even though amber is similar to gold, some people have russet- or copper-colored amber eyes that are mistaken for hazel, though hazel tends to be duller and contains green with red/gold flecks, as mentioned above. Amber eyes may also contain amounts of very light gold-ish gray.

The eyes of some pigeons contain yellow fluorescing pigments known as [[pteridine]]s.<ref>{{cite journal |author=Oliphant LW |title=Observations on the pigmentation of the pigeon iris |journal=Pigment Cell Res. |volume=1 |issue=3 |pages=202–8 |year=1987 |pmid=3508278 |doi=10.1111/j.1600-0749.1987.tb00414.x }}</ref> The bright yellow eyes of the [[great horned owl]] are thought to be due to the presence of the pteridine pigment [[xanthopterin]] within certain [[chromatophore]]s (called xanthophores) located in the iris stroma.<ref>{{cite journal |author=Oliphant LW |title=Crystalline pteridines in the stromal pigment cells of the iris of the great horned owl |journal=Cell Tissue Res. |volume=217 |issue=2 |pages=387–95 |year=1981 |pmid=7237534 |doi=10.1007/BF00233588 |s2cid=8061493 }}</ref> In humans, yellowish specks or patches are thought to be due to the pigment [[lipofuscin]], also known as lipochrome.<ref name=Lefohn/> Many animals such as canines, domestic cats, owls, eagles, pigeons, and fish have amber eyes, whereas in humans this color occurs less frequently. Amber is the third-rarest natural eye color after green and gray, occurring in 5% of the world's population.<ref>{{Cite web|title=Amber eyes|url=https://www.allaboutvision.com/eye-care/eye-anatomy/amber-eyes/|access-date=2021-05-09|website=All About Vision|language=en-us}}</ref> People with amber-colored eyes are found in [[Europe]], and in fewer numbers in the [[Middle East]], [[North Africa]], and [[South America]].<ref>{{Cite journal |last1=Ruiz-Linares |first1=Andrés |last2=Adhikari |first2=Kaustubh |last3=Acuña-Alonzo |first3=Victor |last4=Quinto-Sanchez |first4=Mirsha |last5=Jaramillo |first5=Claudia |last6=Arias |first6=William |last7=Fuentes |first7=Macarena |last8=Pizarro |first8=María |last9=Everardo |first9=Paola |last10=de Avila |first10=Francisco |last11=Gómez-Valdés |first11=Jorge |last12=León-Mimila |first12=Paola |last13=Hunemeier |first13=Tábita |last14=Ramallo |first14=Virginia |last15=Silva de Cerqueira |first15=Caio C. |date=2014-09-25 |title=Admixture in Latin America: Geographic Structure, Phenotypic Diversity and Self-Perception of Ancestry Based on 7,342 Individuals |journal=PLOS Genetics |volume=10 |issue=9 |pages=e1004572 |doi=10.1371/journal.pgen.1004572 |issn=1553-7390 |pmc=4177621 |pmid=25254375 |doi-access=free |bibcode=2014PLOSG..10.4572R }}</ref>

===Hazel===
[[File:Extreme close-up shot of the eye of Cuban news anchor Armando Ramirez Diaz.jpg|thumb|Hazel eye]]
[[File:Hazel Eye HD.JPG|thumb|Hazel eye]]
The hazel color of eyes is caused by a combination of [[Rayleigh scattering]] and a moderate amount of melanin in the iris' anterior border layer.<ref name=Wang/><ref name=Lefohn>{{cite journal |vauthors=Lefohn A, Budge B, Shirley P, Caruso R, Reinhard E |title=An Ocularist's Approach to Human Iris Synthesis |journal=IEEE Comput. Graph. Appl. |volume=23 |issue=6 |pages=70–5 |year=2003 |doi=10.1109/MCG.2003.1242384 |s2cid=537404 |url=https://escholarship.org/uc/item/8d88d3qc }}</ref> Hazel eyes often appear to shift in color from a brown to a green. Although hazel mostly consists of brown and green, the dominant color in the eye can either be brown/gold or green. This is why hazel eyes can be mistaken as amber, and why amber is often counted as hazel in studies, and vice versa.<ref name=Zhu>{{cite journal |title=A genome scan for eye color in 502 twin families: most variation is due to a QTL on chromosome 15q |journal=Twin Res |volume=7 |issue=2 |pages=197–210 |year=2004 |pmid=15169604 |doi=10.1375/136905204323016186 |last1=Zhu |first1=Gu |last2=Evans |first2=David M. |last3=Duffy |first3=David L. |last4=Montgomery |first4=Grant W. |last5=Medland |first5=Sarah E.|author-link5=Sarah Medland |last6=Gillespie |first6=Nathan A. |last7=Ewen |first7=Kelly R. |last8=Jewell |first8=Mary |last9=Liew |first9=Yew Wah |first10=Nicholas K. |last10=Hayward |first11=Richard A. |last11=Sturma |first12=Jeffrey M. |last12=Trenta |first13=Nicholas G. |last13=Martina|doi-access=free }}</ref><ref>{{cite journal |last1=Albert |first1=Daniel M |last2=Green |first2=W Richard |last3=Zimbric |first3=Michele L |last4=Lo |first4=Cecilia |last5=Gangnon |first5=Ronald E |last6=Hope |first6=Kirsten L |last7=Gleiser |first7=Joel |title=Iris melanocyte numbers in Asian, African American, and Caucasian irides. |journal=Transactions of the American Ophthalmological Society |date=2003 |volume=101 |pages=217–222 |pmid=14971580 |pmc=1358991 }}</ref><ref name=Mitchell>{{cite journal |vauthors=Mitchell R, Rochtchina E, Lee A, Wang JJ, Mitchell P |title=Iris color and intraocular pressure: the Blue Mountains Eye Study |journal=Am. J. Ophthalmol. |volume=135 |issue=3 |pages=384–6 |year=2003 |pmid=12614760 |doi=10.1016/S0002-9394(02)01967-0 |url=https://ur.booksc.eu/dl/17418414/f57a1f }}</ref><ref>{{cite journal |vauthors=Lindsey JD, Jones HL, Hewitt EG, Angert M, Weinreb RN |title=Induction of tyrosinase gene transcription in human iris organ cultures exposed to latanoprost |journal=Arch. Ophthalmol. |volume=119 |issue=6 |pages=853–60 |year=2001|pmid=11405836 |doi=10.1001/archopht.119.6.853|doi-access=free }}</ref><ref name=Frank>{{cite journal |vauthors=Frank RN, Puklin JE, Stock C, Canter LA |title=Race, iris color, and age-related macular degeneration |journal=Trans Am Ophthalmol Soc |volume=98 |pages=109–15; discussion 115–7 |year=2000 |pmid=11190014 |pmc=1298217 }}</ref><ref name=Regan>{{cite journal |vauthors=Regan S, Judge HE, Gragoudas ES, Egan KM |title=Iris color as a prognostic factor in ocular melanoma |journal=Arch. Ophthalmol. |volume=117 |issue=6 |pages=811–4 |year=1999 |pmid=10369595 |doi=10.1001/archopht.117.6.811|doi-access=free }}</ref><ref>{{cite journal |vauthors=Hawkins TA, Stewart WC, McMillan TA, Gwynn DR |title=Analysis of diode, argon, and Nd: YAG peripheral iridectomy in cadaver eyes |journal=Doc Ophthalmol |volume=87 |issue=4 |pages=367–76 |year=1994 |pmid=7851220 |doi=10.1007/BF01203345 |s2cid=30893783 }}</ref> The combination can sometimes produce a multicolored iris, i.e. an eye that is light brown/amber near the pupil and charcoal or dark green on the outer part of the iris (or vice versa) when observed in sunlight.

Definitions of the eye color "hazel" vary: it is sometimes considered to be synonymous with light brown or gold, as in the color of a [[hazelnut]] shell.<ref name=Zhu /><ref name=Mitchell /><ref name=Regan /><ref name=Hammond>{{cite journal |vauthors=Hammond BR, Fuld K, Snodderly DM |title=Iris color and macular pigment optical density |journal=Exp. Eye Res. |volume=62 |issue=3 |pages=293–7 |year=1996 |pmid=8690039 |doi=10.1006/exer.1996.0035}}</ref>

Around 18% of the US population and 5% of the world population have hazel eyes.<ref name=":0" /> 55.2% of Spanish subjects in a series of 221 photographs were judged to have hazel eyes.<ref name="pubmed"/> Hazel eyes are found in [[Europe]], most commonly in the [[Netherlands]] and the [[United Kingdom]],<ref>{{cite web | url=https://www.coalitionbrewing.com/where-are-hazel-eyes-most-common/ | title=Where are hazel eyes most common? | date=26 February 2023 }}</ref> and have also been observed to be very common among the [[Low Saxon]]-speaking populations of northern Germany.<ref>{{cite book |last1=Beddoe |first1=John |title=The Races of Britain. A contribution to the anthropology of Western Europe |date=1971 |publisher=Michigan State University |isbn=9780091013707 |page=39 |url=https://books.google.com/books?id=7z06AQAAMAAJ |language=en |quote=the Saxons...being very often hazel-eyed}}</ref>

===Green===
{{misleading|section|date=August 2023}}
[[File:Greeneyes.jpg|thumb|Green eyes]]
Green eyes probably result from the interaction of multiple allelic variants of ''[[OCA2]]'' and other genes. They may have been present in southern [[Siberia]] during the [[Bronze Age]].<ref name=bronzeage>{{cite journal |last1=Keyser |first1=Christine |last2=Bouakaze |first2=Caroline |last3=Crubézy |first3=Eric |last4=Nikolaev |first4=Valery G. |last5=Montagnon |first5=Daniel |last6=Reis |first6=Tatiana |last7=Ludes |first7=Bertrand |year=2009 |title=Ancient DNA Provides New Insights into the History of South Siberian Kurgan People |journal=Human Genetics |volume=126 |issue=3 |pages=395–410 |doi=10.1007/s00439-009-0683-0 |pmid=19449030 |s2cid=21347353 |quote=Indeed, among the SNPs tested was rs12913832, a single DNA variation within a regulatory element of HERC2 gene which is associated to blue eye color in humans. This polymorphism, together with the diplotypes obtained from variations of the OCA2 locus (major contributor to the human eye color variation) showed that at least 60% of the ancient Siberian specimens under study had blue (or green) eyes.}}</ref>

Green eyes are most common in [[Northern Europe|Northern]], [[Western Europe|Western]], and [[Central Europe]].<ref>[http://www.eyedoctorguide.com/eye_general/eye_color.html Blue Eyes Versus Brown Eyes: A Primer on Eye Color] {{Webarchive|url=https://web.archive.org/web/20081017164118/http://www.eyedoctorguide.com/eye_general/eye_color.html |date=17 October 2008 }}. Eyedoctorguide.com. Retrieved on 23 December 2011.</ref><ref>[http://cogweb.ucla.edu/ep/Frost_06.html Why Do Europeans Have So Many Hair and Eye Colors?]. Cogweb.ucla.edu. Retrieved on 23 December 2011.</ref> Around 8–10% of men and 18–21% of women in [[Iceland]] and 6% of men and 17% of women in the [[Netherlands]] have green eyes.<ref name="sulem">{{cite journal |last1=Sulem|first1=P.|last2= Gudbjartsson|first2=D. |display-authors=et al.|title=Genetic determinants of hair, eye and skin pigmentation in Europeans |journal=Nature Genetics |year=2007 |volume=39 |issue=12 |pages=1443–1452 |doi=10.1038/ng.2007.13 |pmid=17952075 |s2cid=19313549 |url=https://www.researchgate.net/publication/5893814 |access-date=21 February 2022}}</ref> Among [[European Americans]], green eyes are most common among those of recent [[Celts (modern)|Celtic]] and [[Germanic peoples|Germanic]] ancestry, occurring in about 16% of people with those backgrounds.<ref name=sulem/>

The green color is caused by the combination of: 1) an amber or light brown pigmentation in the stroma of the iris (which has a low or moderate concentration of melanin), and 2) a blue shade created by the Rayleigh scattering of reflected light.<ref name="Fox"/> Green eyes contain the yellowish pigment [[lipochrome]].<ref>[http://allaboutgenes.weebly.com/oca2.html "OCA2: The Gene for Color"] {{Webarchive|url=https://web.archive.org/web/20161006151409/http://allaboutgenes.weebly.com/oca2.html |date=6 October 2016 }}. allaboutgenes.weebly.com. Retrieved on 8 September 2016.</ref>
<!---[[File:Chinchilla Persian cat with sea-green eyes.jpg|thumb|A [[Chinchilla Persian]] with sea-green eyes]]--->

===Blue===
{{Redirect|Blue eyes}}
[[File:Blue eye 2.jpg|thumb|A light blue iris with [[limbal ring]]]]
[[File:A blue eye.jpg|thumb|Blue iris]]
There is no intrinsically blue pigmentation either in the iris or in the [[vitreous body]]; in fact, a form of melanin that would produce a blue coloration does not currently exist in the bodies of most mammals. Rather, blue eyes result from [[structural color]] in combination with certain concentrations of non-blue pigments. The iris pigment [[epithelium]] is brownish black due to the presence of [[melanin]].<ref name=Menon>{{cite journal |vauthors=Menon IA, Basu PK, Persad S, Avaria M, Felix CC, Kalyanaraman B |title=Is there any difference in the photobiological properties of melanins isolated from human blue and brown eyes? |journal=Br J Ophthalmol |volume=71 |issue=7 |pages=549–52 |year=1987|pmid=2820463 |pmc=1041224 |doi=10.1136/bjo.71.7.549}}</ref> Unlike brown eyes, blue eyes have low concentrations of melanin in the stroma of the iris, which lies in front of the dark epithelium. Longer wavelengths of light tend to be absorbed by the dark underlying epithelium, while shorter wavelengths are reflected and undergo [[Rayleigh scattering]] in the [[Turbidity|turbid]] medium of the stroma.<ref name="Wang"/> This is the same scattering that accounts for the blue appearance of the sky.<ref name="Fox1978"/>{{rp|9}}<ref name="Mason"/> The result is a "[[Tyndall effect|Tyndall]] blue" structural color that varies with external lighting conditions.
 	
Blue eyes are a highly [[sexually dimorphic]] eye color. Studies from various populations in Europe have shown that men are substantially more likely to have blue eyes than women.<ref name="Martinez-Cadenas Peña-Chilet Ibarrola-Villava Ribas 2013 pp. 453–460" />

The inheritance pattern followed by blue eyes was previously assumed to be a [[Mendelian inheritance|Mendelian recessive]] trait, though this has been shown to be incorrect. Eye color inheritance is now recognized as a [[polygenic trait]], meaning that it is controlled by the interactions of several genes.<ref>{{harvnb|Duffy|Montgomery|Chen|Zhao|Le|Hayward|Martin|Sturm|2007|quote=The genetics of human eye color has been studied for over a century,52 and, for most of that time, it was considered a simple Mendelian recessive trait, with brown eye color dominant over blue. More recently, eye color has been accepted as being a polygenic trait, with multiple genes contributing to the expressivity of eye color.18,35}}</ref>

In 2008, a team of researchers from the [[University of Copenhagen]] located a single mutation that causes the phenomenon of blue eyes. The research was published in the ''[[Journal of Human Genetics]]''. The same DNA sequence of the ''OCA2'' gene among blue-eyed people suggests they may have a single common ancestor. The researchers hypothesized that the ''OCA2'' mutation responsible for blue eyes arose in an individual who lived in the northwestern part of the [[Black Sea]] region in [[Europe]] sometime between 6,000 and 10,000 years ago, during the [[Neolithic]] period.<ref name="MSNBC">{{cite news|first=Jeanna|last=Bryner|title= Genetic mutation makes those brown eyes blue|publisher=[[NBC News]] |date=31 January 2008|access-date=19 October 2009|url=http://www.nbcnews.com/id/22934464|archive-url=https://web.archive.org/web/20130701044221/http://www.nbcnews.com/id/22934464|url-status=dead|archive-date=1 July 2013}}</ref><ref>{{cite web |date=2008-01-31 |title=How one ancestor helped turn our brown eyes blue |url=https://www.independent.co.uk/news/science/how-one-ancestor-helped-turn-our-brown-eyes-blue-776170.html |access-date=2015-12-21 |website=The Independent |language=en-GB}} "Everyone with blue eyes alive today can trace their ancestry back to one person who probably lived about 10,000 years ago in the Black Sea region, a study has found."</ref> However, more recent [[ancient DNA]] research has identified human remains much older than the Neolithic period which possess the ''OCA2'' mutation for blue eyes. It is now believed that the ''OCA2'' allele responsible for blue eyes dates back to the migration of modern humans [[Recent African origin of modern humans|out of Africa]] roughly 50,000 years ago, and entered Europe from western Asia.<ref name="Cberg" />

Eiberg and colleagues suggested in a study published in ''Human Genetics'' that a mutation in the 86th [[intron]] of the ''[[HERC2]]'' gene, which is hypothesized to interact with the ''OCA2'' gene [[Promoter (biology)|promoter]], reduced expression of ''OCA2'' with subsequent reduction in melanin production.<ref name="MSNBC" /><ref name="blue mutation">{{cite journal |last1=Eiberg |first1=Hans |last2=Troelsen |first2=Jesper |last3=Nielsen |first3=Mette |last4=Mikkelsen |first4=Annemette |last5=Mengel-From |first5=Jonas |last6=Kjaer |first6=Klaus W. |last7=Hansen |first7=Lars |year=2008 |title=Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression |journal=Hum. Genet. |volume=123 |issue=2 |pages=177–87 |doi=10.1007/s00439-007-0460-x |pmid=18172690 |s2cid=9886658}}</ref><ref name="telegraph.co.uk">{{cite news |url=https://www.telegraph.co.uk/science/science-news/3323607/Blue-eyes-result-of-ancient-genetic-mutation.html |archive-url=https://web.archive.org/web/20091101055254/http://www.telegraph.co.uk/science/science-news/3323607/Blue-eyes-result-of-ancient-genetic-mutation.html |archive-date=1 November 2009 |location=London |work=The Daily Telegraph |title=Blue eyes result of ancient genetic 'mutation' |first=Roger |last=Highfield |date=30 January 2008 |access-date=19 October 2011}}</ref>

It has been proposed that blue eyes may have been adaptive to shorter day lengths at higher latitudes, as blue eyes increase intraocular light scattering, which suppresses [[melatonin]] release from the [[pineal gland]], perhaps reducing psychological depression (which is linked to the short day length of higher latitudes).<ref name="e300">{{cite journal | last=Lucock | first=Mark D. | title=The evolution of human skin pigmentation: A changing medley of vitamins, genetic variability, and <scp>UV</scp> radiation during human expansion | journal=American Journal of Biological Anthropology | publisher=Wiley | volume=180 | issue=2 | date=2022-06-25 | issn=2692-7691 | doi=10.1002/ajpa.24564 | pages=252–271| pmid=36790744 |quote=This may also be a direct counter‐measure to a short winter photoperiod at high latitudes; blue eyes increase intraocular light scattering and thereby suppress melatonin release from the pineal gland. This may be an adaptive trait to reduce/prevent depression, a condition linked to short day length (Higuchi et al., 2007; Lucock et al., 2021).| pmc=10083917 }}</ref>

Blue eyes are predominant in northern and eastern Europe, particularly around the [[Baltic Sea]]. Blue eyes are also found in [[Southern Europe]], [[Central Asia]], [[South Asia]], [[North Africa]], and [[West Asia]].<ref name="Cavalli-Sforza, L. L. 1994">{{cite book |last1=Cavalli-Sforza |first1=Luigi Luca |last2=Cavalli-Sforza |first2=Luca |last3=Menozzi |first3=Paolo |last4=Piazza |first4=Alberto |title=The History and Geography of Human Genes |url=https://archive.org/details/historygeography0000cava_g9l7 |url-access=registration |date=1994 |publisher=Princeton University Press |isbn=978-0-691-08750-4 }}{{page needed|date=May 2020}}</ref><ref name="altervista1">{{cite web|url=http://carnby.altervista.org/troe/08-05.htm |title=Distribution of Bodily Characters. Pigmentation, the Pilous System, and Morphology of the Soft Parts |archive-url=https://web.archive.org/web/20110726095519/http://carnby.altervista.org/troe/08-05.htm |archive-date=26 July 2011 }}</ref>
<!---
<gallery widths="200" heights="160px">
File:Bimbam.jpg|A [[Birman|Birman kitten]] with distinctive [[sapphire]] blue eyes
File:Karasu2a.JPG|[[Jungle crow]]
File:FrankieakaLogan.jpg|The first blue-eyed [[koala]] known to be born in captivity<ref>[http://www.adelaidenow.com.au/worlds-only-blue-eyed-koala/story-e6frea6u-1111115302021 Blue eyed Koala]. Adelaidenow.com.au (11 January 2008). Retrieved on 2011-12-23.</ref>
File:Blue-eyed black lemur.jpg|[[Sclater's lemur]], also known as the blue-eyed black lemur
</gallery>
--->
Approximately 8% to 10% of the global population have blue eyes.<ref name=":0" /> A 2002 study found the prevalence of blue eye color among the [[White Americans|white population]] in the United States to be 33.8% for those born from 1936 through 1951, compared with 57.4% for those born from 1899 through 1905.<ref name="Grant" /> {{as of|2006}}, one out of every six Americans, or 16.6% of the total US population, has blue eyes,<ref>{{Cite news|last=Belkin|first=Douglas|date=2006-10-18|title=Blue eyes are increasingly rare in America - Americas - International Herald Tribune (Published 2006)|language=en-US|work=The New York Times|url=https://www.nytimes.com/2006/10/18/world/americas/18iht-web.1018eyes.3199975.html|access-date=2021-02-02|issn=0362-4331}}</ref> including 22.3% of whites. The incidence of blue eyes continues to decline among American children.<ref name="BostonGlobe">{{cite web |url=http://www.boston.com/yourlife/articles/2006/10/17/dont_it_make_my_blue_eyes_brown/ |title=Don't it make my blue eyes brown Americans are seeing a dramatic color change|work=The Boston Globe |date=17 October 2006 |first=Douglas |last=Belkin |archive-url=https://web.archive.org/web/20141022125010/http://www.boston.com/yourlife/articles/2006/10/17/dont_it_make_my_blue_eyes_brown/?page=2 |archive-date=22 October 2014}}</ref> Of [[Slovenes]], 56% have blue/green eyes.<ref>{{cite journal|title= Prediction of eye color in the Slovenian population using the IrisPlex SNPs| pmc=3760663 | pmid=23986280 | volume=54 | issue=4 | year=2013 | journal=Croat. Med. J. | pages=381–6 | last1 = Kastelic | first1 = V | last2 = Pośpiech | first2 = E | last3 = Draus-Barini | first3 = J | last4 = Branicki | first4 = W | last5 = Drobnič | first5 = K | doi=10.3325/cmj.2013.54.381}}</ref> In a series of 221 photographs of Spanish subjects, 16.3% of the subjects were determined to have blue-gray eyes.<ref name="pubmed">{{Cite journal |last1=Muiños Díaz |first1=Yerena |last2=Saornil |first2=Maria A. |last3=Almaraz |first3=Ana |last4=Muñoz-Moreno |first4=Mari F. |last5=García |first5=Ciro |last6=Sanz |first6=Ruperto |date=2009 |title=Iris color: validation of a new classification and distribution in a Spanish population-based sample |url=https://pubmed.ncbi.nlm.nih.gov/19551689/ |journal=European Journal of Ophthalmology |volume=19 |issue=4 |pages=686–689 |doi=10.1177/112067210901900427 |issn=1120-6721 |pmid=19551689|s2cid=40940828 }}</ref>

===Gray===
[[File:Gray eye, Northern Italy.jpg|thumb|Gray eye]]
Like blue eyes, gray eyes have a dark epithelium at the back of the iris and a relatively clear stroma at the front. One possible explanation for the difference in appearance between gray and blue eyes is that gray eyes have larger deposits of [[collagen]] in the stroma, so that the light that is reflected from the epithelium undergoes [[Mie scattering]] (which is not strongly frequency-dependent) rather than Rayleigh scattering (in which shorter wavelengths of light are scattered more). This would be analogous to the change in the color of the sky, from the blue given by the Rayleigh scattering of sunlight by small gas molecules when the sky is clear, to the gray caused by Mie scattering of large water droplets when the sky is cloudy.<ref name="Southworth">{{cite web |url=http://www.thetech.org/genetics/ask.php?id=232 |title=Are gray eyes the same as blue in terms of genetics? |work=Understanding Genetics: Human Health and the Genome |publisher=Stanford School of Medicine |author=Lucy Southworth |access-date=19 October 2011 |archive-url=https://web.archive.org/web/20110927085904/http://www.thetech.org/genetics/ask.php?id=232 |archive-date=27 September 2011 }}</ref> Alternatively, it has been suggested that gray and blue eyes might differ in the concentration of melanin at the front of the stroma.<ref name="Southworth" />

Gray eyes can also be found among the [[Algeria]]n [[Shawia people]]<ref>{{in lang|fr}}  [https://books.google.com/books?id=7rwBAAAAYAAJ&pg=PA272 Provincia: bulletin trimestriel de la Société de Statistique ...], Volumes 16–17 By Société de statistique, d'histoire et d'archéologie de Marseille et de Provence p. 273 ''l'iris gris est celui des chaouias...''</ref> of the [[Aurès Mountains]] in Northwest Africa, in the [[Middle East]]/[[West Asia]], [[Central Asia]], and [[South Asia]]. In the ''[[Iliad]]'', the Greek goddess [[Athene]] is said to have gray eyes (γλαυκῶπις).<ref>''[[Iliad]]'' 1:206 http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.01.0133%3Abook%3D1%3Acard%3D206</ref> Under magnification, gray eyes exhibit small amounts of yellow and brown color in the iris.

Gray is the second-rarest natural eye color after green, with 3% of the world's population having it.<ref>{{Cite web|title=Gray eyes|url=https://www.allaboutvision.com/eye-care/eye-anatomy/gray-eyes/|access-date=2021-05-09|website=All About Vision|language=en-us}}</ref>

=== Special cases ===
==== Two different colors ====
[[File:Heterochromia_Iridis.jpg|thumb|Two different eye colors are known as [[heterochromia iridum]]]]
As a result of [[heterochromia iridum]], it is also possible to have two different eye colors. This occurs in humans and certain breeds of domesticated animals and affects less than 1 percent of the world's population.<ref name=":3" />

====Red and violet====
[[File:OCA1 Auge.jpg|thumb|Red-appearing albino eyes]]
The eyes of people with severe forms of [[albinism in humans|albinism]] may appear red under certain lighting conditions owing to the extremely low quantities of [[melanin]],<ref name="albinism">[http://www.albinism.org/publications/what_is_albinism.html NOAH – What is Albinism?] {{webarchive|url=https://web.archive.org/web/20120514003907/http://albinism.org/publications/what_is_albinism.html |date=14 May 2012 }}. Albinism.org. Retrieved on 23 December 2011.</ref> allowing the blood vessels to show through. In addition, [[flash photography]] can sometimes cause a "[[red-eye effect]]", in which the very bright light from a flash reflects off the retina, which is abundantly vascular, causing the pupil to appear red in the photograph.<ref>
{{cite news |title=HOW TO: Avoid the red eye effect |author=Dave Johnson |newspaper=[[PC World (magazine)#Countries|New Zealand PC World]] |date=16 January 2009 |url=http://pcworld.co.nz/pcworld/pcw.nsf/digi/D193D7DD8DD78628CC257540000F4A4F |access-date=9 January 2010 |archive-url=https://web.archive.org/web/20100224065704/http://pcworld.co.nz/pcworld/pcw.nsf/digi/D193D7DD8DD78628CC257540000F4A4F |archive-date=24 February 2010 }}
</ref>

Although the deep blue eyes of some people such as [[Elizabeth Taylor]] can appear purple or violet at certain times, "true" violet-colored eyes occur only due to albinism.<ref name="palmer20110325">{{cite web |url=http://www.slate.com/blogs/blogs/browbeat/archive/2011/03/25/elizabeth-taylor-beautiful-mutant.aspx |archive-url=https://web.archive.org/web/20110327113617/http://www.slate.com/blogs/blogs/browbeat/archive/2011/03/25/elizabeth-taylor-beautiful-mutant.aspx |archive-date=27 March 2011 |title=Elizabeth Taylor: Beautiful Mutant |access-date=26 March 2011 |author=Palmer, Roxanne |date=25 March 2005 |work=Slate}}</ref><ref name="Albinism">{{cite encyclopedia |last1=Fertl |first1=Dagmar |last2=Rosel |first2=Patricia |title=Albinism |encyclopedia=Encyclopedia of Marine Mammals |edition=Second |entry=Albinism |publisher=Academic Press |date=2009 |pages=24–26 |doi=10.1016/b978-0-12-373553-9.00006-7 |isbn=978-0-12-373553-9 |entry-url=https://www.sciencedirect.com/science/article/pii/B9780123735539000067 |access-date=11 October 2022}}</ref><ref>{{cite journal |last1=White |first1=Désirée |last2=Rabago-Smith |first2=Montserrat |title=Genotype–phenotype associations and human eye color |journal=Journal of Human Genetics |date=2010 |volume=56 |issue=1 |pages=5–7 |doi=10.1038/jhg.2010.126 |pmid=20944644 |s2cid=33808164 |doi-access=free }}</ref> Eyes that appear red or violet under certain conditions due to albinism occur in less than 1 percent of the world's population.<ref name=":3">{{Cite web|title=The World's Population By Eye Color|url=https://www.worldatlas.com/articles/which-eye-color-is-the-most-common-in-the-world.html|access-date=2021-05-10|website=WorldAtlas|date=6 October 2020|language=en-US}}</ref>