Editing Blue (section)

===Eyes===
{{main|Eye colour#Blue}}
[[File:A blue eye.jpg|thumb|right|150px|Blue eyes actually contain no blue pigment. The colour is caused by an effect called [[Tyndall effect|Tyndall scattering]].]]
Blue eyes do not actually contain any blue pigment. [[Eye colour]] is determined by two factors: the [[pigment]]ation of the eye's [[Iris (anatomy)|iris]]<ref name="Wielgus">{{Cite journal |vauthors=Wielgus AR, Sarna T |year=2005 |title=Melanin in human irides of different color and age of donors |journal=Pigment Cell Res. |volume=18 |issue=6 |pages=454–64 |doi=10.1111/j.1600-0749.2005.00268.x |pmid=16280011}}</ref><ref name="Prota">{{Cite journal |vauthors=Prota G, Hu DN, Vincensi MR, McCormick SA, Napolitano A |year=1998 |title=Characterization of melanins in human irides and cultured uveal melanocytes from eyes of different colors |journal=Exp. Eye Res. |volume=67 |issue=3 |pages=293–99 |doi=10.1006/exer.1998.0518 |pmid=9778410|doi-access=free }}</ref> and the [[scattering]] of light by the [[Turbidity|turbid]] medium in the [[Stroma of iris|stroma of the iris]].<ref name="Fox">{{Cite book |last=Fox |first=Denis Llewellyn |url=https://books.google.com/books?id=c2xyxwlm2UkC&pg=PA9 |title=Biochromy: Natural Coloration of Living Things |publisher=University of California Press |year=1979 |isbn=978-0-520-03699-4 |page=9 |archive-url=https://web.archive.org/web/20151003232604/https://books.google.com/books?id=c2xyxwlm2UkC&pg=PA9 |archive-date=3 October 2015 |url-status=live}}</ref> In humans, the pigmentation of the iris varies from light brown to black. The appearance of blue, green, and hazel eyes results from the [[Tyndall effect|Tyndall scattering]] of light in the stroma, an optical effect similar to what accounts for the blueness of the sky.<ref name="Fox" /><ref name="Mason">{{Cite journal |last=Mason |first=Clyde W. |year=1924 |title=Blue Eyes |journal=Journal of Physical Chemistry |volume=28 |issue=5 |pages=498–501 |doi=10.1021/j150239a007}}</ref> The irises of the eyes of people with blue eyes contain less dark [[melanin]] than those of people with brown eyes, which means that they absorb less short-wavelength blue light, which is instead reflected out to the viewer. Eye colour also varies depending on the lighting conditions, especially for lighter-coloured eyes.

Blue eyes are most common in Ireland, the [[Baltic Sea]] area and [[Northern Europe]],<ref name="BostonGlobe" /> and are also found in [[Eastern Europe|Eastern]], [[Central Europe|Central]], and [[Southern Europe]]. Blue eyes are also found in parts of [[Western Asia]], most notably in [[Afghanistan]], [[Syria]], [[Iraq]], and [[Iran]].<ref name="altervista1">{{Cite web |title=Pigmentation, the Pilous System, and Morphology of the Soft Parts |url=http://carnby.altervista.org/troe/08-05.htm |archive-url=https://web.archive.org/web/20110726095519/http://carnby.altervista.org/troe/08-05.htm |archive-date=26 July 2011 |website=altervista.org}}</ref> In [[Estonia]], 99% of people have blue eyes.<ref>statement by Hans Eiberg from the Department of Cellular and Molecular Medicine at the [[University of Copenhagen]]</ref><ref name="More than">{{Cite web |last=Weise |first=Elizabeth |date=5 February 2008 |title=More than meets the blue eye: You may all be related |url=https://www.usatoday.com/news/health/2008-02-05-blue-eyes_N.htm |archive-url=https://web.archive.org/web/20120910205153/http://www.usatoday.com/news/health/2008-02-05-blue-eyes_N.htm |archive-date=10 September 2012 |access-date=23 December 2011 |website=USA TODAY}}</ref> In [[Denmark]] in 1978, only 8% of the population had brown eyes, though through immigration, today that number is about 11%.<ref name="More than" /> In [[Germany]], about 75% have blue eyes.<ref name="More than" />

In the United States, as of 2006, 1 out of every 6 people, or 16.6% of the total population, and 22.3% of the [[White Americans|white population]], have blue eyes, compared with about half of Americans born in 1900, and a third of Americans born in 1950. Blue eyes are becoming less common among American children{{Citation needed|date=November 2022}}. In the US, males are 3–5% more likely to have blue eyes than females.<ref name="BostonGlobe">{{Cite web |last=Douglas Belkin |date=17 October 2006 |title=Don't it make my blue eyes brown Americans are seeing a dramatic color change |url=https://www.boston.com/yourlife/articles/2006/10/17/dont_it_make_my_blue_eyes_brown/ |url-status=live |archive-url=https://web.archive.org/web/20120223022627/http://www.boston.com/yourlife/articles/2006/10/17/dont_it_make_my_blue_eyes_brown/ |archive-date=23 February 2012 |website=The Boston Globe}}</ref>