Editing Heterochromia iridum (section)

==Background==
[[File:Khao Manee Lily (cropped 2).jpg|thumb|[[Khao Manee]] [[odd-eyed cat|cat with complete heterochromia]], and central heterochromia in both eyes.]]
[[Eye color]], specifically the color of the irises, is determined primarily by the concentration and distribution of melanin. Although the processes determining eye color are not fully understood, it is known that inherited eye color is determined by multiple [[genes]]. Environmental or acquired factors can alter these inherited traits.<ref name="Wielgus">{{cite journal |vauthors=Wielgus AR, Sarna T |title=Melanin in human irides of different color and age of donors |journal=Pigment Cell Research|volume=18 |issue=6 |pages=454–64 |date=December 2005 |pmid=16280011 |doi=10.1111/j.1600-0749.2005.00268.x}}</ref>

The color of the mammalian, including human, iris is very variable. However, there are only two pigments present, [[eumelanin]] and [[pheomelanin]]. The overall concentration of these pigments, the ratio between them, variation in the distribution of pigment in the layers of the stroma of the iris and the effects of light scattering all play a part in determining eye color.<ref name="Prota">{{cite journal |vauthors=Prota G, Hu DN, Vincensi MR, McCormick SA, Napolitano A |title=Characterization of melanins in human irides and cultured uveal melanocytes from eyes of different colors |journal=Experimental Eye Research|volume=67 |issue=3 |pages=293–9 |date=September 1998 |pmid=9778410 |doi=10.1006/exer.1998.0518}}</ref> In the United States, July 12 is observed by some as National Different Colored Eyes Day.<ref name="Different Colored Eyes Day">National Day Calendar [https://nationaldaycalendar.com/national-different-colored-eyes-day-july-12/ "National Different Colored Eyes Day - July 12"] {{webarchive|url=https://web.archive.org/web/20230331022026/https://nationaldaycalendar.com/national-different-colored-eyes-day-july-12/|date=2023-03-31}} ''National Day Calendar.'' November 8, 2022. Retrieved July 12, 2023.</ref>