Editing Color blindness (section)

==Effects==
{{How-to|section|date=December 2024}}
A color blind person will have decreased (or no) color discrimination along the red–green axis, blue–yellow axis, or both. However, the vast majority of the color blind are only affected on their red–green axis.

The first indication of color blindness generally consists of a person using the wrong color for an object, such as when painting, or calling a color by the wrong name. The colors that are confused are very consistent among people with the same type of color blindness.

<gallery>
File:Вечір на "інтегралі" - річка Південний Буг.jpg|Normal sight
File:Deuteranopia sight.jpg|Deuteranopic sight
File:Protanopia sight.png|Protanopic sight
File:Tritanopia sight.jpg|Tritanopic sight
File:Monochromacy sight.jpg|Monochromatic sight
</gallery>

===Confusion colors===
[[File:Color Blind Confusion Lines.png|thumb|upright=1.8|Confusion lines for the three types of dichromacy superimposed on CIEXYZ color space]]
Confusion colors are pairs or groups of colors that will often be mistaken by the color blind. Confusion colors for red–green color blindness include:
* cyan and grey
* [[rose (color)|rose-pink]] and grey
* blue and purple
* yellow and [[Shades of green#Neon green|neon green]]
* red, green, orange, brown
Confusion colors for tritan include:
* yellow and grey
* blue and green
* dark blue/violet and black
* violet and yellow-green
* red and [[Rose (color)|rose-pink]]
These colors of confusion are defined quantitatively by straight confusion lines plotted in [[CIEXYZ]], usually plotted on the corresponding [[CIE 1931 color space#CIE xy chromaticity diagram and the CIE xyY color space|chromaticity diagram]]. The lines all intersect at a ''copunctal point'', which varies with the [[#Based on affected cone|type of color blindness]].<ref>{{cite journal |last1=Fomins |first1=S |title=Multispectral analysis of color vision deficiency tests |journal=Materials Science |date=2011 |volume=17 |issue=1 |pages=104–108 |doi=10.5755/j01.ms.17.1.259|doi-access=free }}</ref> [[Chromaticity|Chromaticities]] along a confusion line will appear [[Metamerism (color)|metameric]] to [[#Dichromacy|dichromats]] of that type. [[#Anomalous trichromacy|Anomalous trichromats]] of that type will see the chromaticities as metameric if they are [[Color difference|close enough]], depending on the strength of their CVD. For two colors on a confusion line to be metameric, the chromaticities first have to be made ''isoluminant'', meaning equal in [[lightness]]. Also, colors that may be isoluminant to the [[CIE 1931 color space#CIE standard observer|standard observer]] may not be isoluminant to a person with dichromacy.

===Color tasks===
{{main|Color task}}
Cole describes four color tasks, all of which are impeded to some degree by color blindness:<ref>{{cite journal |last1=Cole |first1=Barry L |title=The handicap of abnormal colour vision |journal=Clinical and Experimental Optometry |date=1972 |volume=55 |issue=8 |pages=304–310 |doi=10.1111/j.1444-0938.1972.tb06271.x}}</ref>
* '''Comparative'''&nbsp;– When multiple colors must be compared, such as with mixing paint
* '''Connotative'''&nbsp;– When colors are given an implicit meaning, such as red = stop
* '''Denotative''' – When identifying colors, for example by name, such as "where is the yellow ball?"
* '''Aesthetic''' – When colors look nice – or convey an emotional response – but do not carry explicit meaning

The following sections describe specific color tasks with which the color blind typically have difficulty.

===Food===
[[File:Assorted Red and Green Apples (deuteranope view).jpg|thumb|Simulation of the normal (top half of photo) and dichromatic (lower half) perception of red and green apples]]
Color blindness causes difficulty with the ''connotative'' color tasks associated with selecting or preparing food. Selecting food for ripeness can be difficult; the green–yellow transition of bananas is particularly hard to identify. It can also be difficult to detect bruises, mold, or rot on some foods, to determine when meat is done by color, to distinguish some varietals, such as a [[Braeburn]] vs. a [[Granny Smith]] apple, or to distinguish colors associated with artificial flavors (e.g. jelly beans, sports drinks).

===Skin color===
{{main|Evolution of color vision in primates#Skin Tone}}
Changes in skin color due to bruising, sunburn, rashes or even blushing are easily missed by the red–green color blind.

===Traffic lights===
{{See also|#Driving}}
[[File:Salzburg - Gnigl - Eichstraße x Parscher Straße - 2020 01 03-2.jpg|thumb|The lack of standard positional clues makes this light difficult to interpret.]]
The colors of [[traffic light]]s can be difficult for the red–green color blindness. This difficulty includes distinguishing red/amber lights from sodium street lamps, distinguishing green lights (closer to cyan) from normal white lights, and distinguishing red from amber lights, especially when there are no positional clues available (see image).

[[File:Tipperary Hill - greenoverred Syracuse, New York.jpg|thumb|A famously inverted traffic light in Syracuse, New York]]
The main coping mechanism to overcome these challenges is to memorize the position of lights. The order of the common triplet traffic light is standardized as red–amber–green from top to bottom or left to right. Cases that deviate from this standard are rare. One such case is a [[Tipperary Hill#Green over red|traffic light in Tipperary Hill]] in [[Syracuse, New York]], which is upside-down (green–amber–red top to bottom) due to the sentiments of its [[Irish American]] community.<ref>{{cite news|title=New documentary uncovers the Irish links to America's Tipperary Hill|url=http://www.thejournal.ie/tipperary-hill-radio-documentary-3063059-Nov2016/|access-date=15 August 2017|agency=TheJournal.ie|date=6 November 2016|url-status=live|archive-url=https://web.archive.org/web/20170815182810/http://www.thejournal.ie/tipperary-hill-radio-documentary-3063059-Nov2016/|archive-date=15 August 2017}}</ref> However, the light has been criticized due to the potential hazard it poses for color blind drivers.<ref>{{cite web|url=https://gizmodo.com/the-story-behind-syracuses-upside-down-traffic-light-1545301615|title=The Story Behind Syracuse's Upside-Down Traffic Light|author=Zhang, Sarah|work=Gizmodo|date=17 March 2014 |url-status=live|archive-url=https://web.archive.org/web/20140916034424/http://gizmodo.com/the-story-behind-syracuses-upside-down-traffic-light-1545301615|archive-date=2014-09-16}}</ref>

[[File:Colourblind traffic signal.JPG|thumb|Horizontal traffic light in [[Halifax, Nova Scotia]], Canada]]
There are other several features of traffic lights available that help accommodate the color blind. British Rail signals use more easily identifiable colors: The red is blood red, the amber is yellow and the green is a bluish color.{{citation needed|date=June 2022}} Most British road traffic lights are mounted vertically on a black rectangle with a white border (forming a "sighting board"), so that drivers can more easily look for the position of the light. In the [[Eastern Canada|eastern provinces of Canada]], traffic lights are sometimes differentiated by shape in addition to color: square for red, diamond for yellow, and circle for green (see image).

===Signal lights===
{{See also|#Occupations}}
[[Navigation light]]s in marine and aviation settings employ red and green lights to signal the relative position of other ships or aircraft. [[Railway signal#Colour light signals|Railway signal lights]] also rely heavily on red–green–yellow colors. In both cases, these color combinations can be difficult for the red–green color blind. [[Farnsworth Lantern Test|Lantern Tests]] are a common means of simulating these light sources to determine not necessarily whether someone is color blind, but whether they can functionally distinguish these specific signal colors. Those who cannot pass this test are generally completely restricted from working on aircraft, ships or rail, for example.

===Fashion===
{{see also|Color of clothing}}
[[Color analysis]] is the analysis of color in its use in fashion, to determine personal color combinations that are most aesthetically pleasing.<ref>{{Cite web |date=2022-01-01 |title=What is Color Analysis? |url=https://londonimageinstitute.com/what-is-color-analysis/ |access-date=2024-02-21 |website=London Image Institute |language=en-US |archive-date=18 May 2024 |archive-url=https://web.archive.org/web/20240518123554/https://londonimageinstitute.com/what-is-color-analysis/ |url-status=live }}</ref> Colors to combine can include clothing, accessories, makeup, hair color, skin color, eye color, etc. Color analysis involves many aesthetic and comparative [[#Color tasks|color task]] that can be difficult for the color blind.

===Art===
Inability to distinguish color does not necessarily preclude the ability to become a celebrated artist. The 20th century expressionist painter [[Clifton Pugh]], three-time winner of Australia's [[Archibald Prize]], on biographical, gene inheritance and other grounds has been identified as a person with protanopia.<ref>{{cite journal | vauthors = Cole BL, Harris RW | title = Colour blindness does not preclude fame as an artist: celebrated Australian artist Clifton Pugh was a protanope | journal = Clinical & Experimental Optometry | volume = 92 | issue = 5 | pages = 421–8 | date = September 2009 | pmid = 19515095 | doi = 10.1111/j.1444-0938.2009.00384.x | s2cid = 21676461 | doi-access = free }}</ref> 19th century French artist [[Charles Méryon]] became successful by concentrating on [[etching]] rather than painting after he was diagnosed as having a red–green deficiency.<ref>{{cite encyclopedia|url=http://www.answers.com/topic/charles-m-ryon|title=Charles Meryon|last=Anon|encyclopedia=Art Encyclopedia. The Concise Grove Dictionary of Art.|publisher=Oxford University Press|access-date=7 January 2010|url-status=live|archive-url=https://web.archive.org/web/20101125063246/http://www.answers.com/topic/charles-m-ryon|archive-date=25 November 2010}}</ref> [[Jin Kim (animator)|Jin Kim]]'s red–green color blindness did not stop him from becoming first an [[animator]] and later a character designer with [[Walt Disney Animation Studios]].<ref name="LeeHyoWon">{{cite news |last1=Lee |first1=Hyo-won |title=Dreams come true, Disney style |url=https://www.koreatimes.co.kr/www/news/art/2014/01/135_87009.html |access-date=25 November 2019 |work=The Korea Times |date=15 May 2011 |archive-date=20 September 2014 |archive-url=https://archive.today/20140920004053/http://www.koreatimes.co.kr/www/news/art/2014/01/135_87009.html |url-status=live }}</ref>

===Advantages===
<!-- Will need to find a better place to put the information in this section -->
Deuteranomals are better at distinguishing shades of [[khaki]],<ref>{{cite news | doi = 10.1038/news051205-1| title = Colour blindness may have hidden advantages| journal = Nature| date = December 5, 2005| last1 = Simonite| first1 = Tom }}</ref> which may be advantageous when looking for predators, food, or camouflaged objects hidden among foliage.<ref name = dimension>{{cite journal |last1=Bosten |first1=J.M. |last2=Robinson |first2=J.D. |last3=Jordan |first3=G. |last4=Mollon |first4=J.D. |title= Multidimensional scaling reveals a color dimension unique to 'color-deficient' observers |journal=Current Biology |date=December 2005 |volume=15 |issue=23 |pages=R950–R952 |doi= 10.1016/j.cub.2005.11.031|pmid=16332521 |s2cid=6966946 |doi-access=free |bibcode=2005CBio...15.R950B }}</ref> Dichromats tend to learn to use texture and shape clues and so may be able to penetrate camouflage that has been designed to deceive individuals with normal color vision.<ref name="Morgan"/><ref>{{cite journal | doi= 10.1038/146226a0 | title=Colour-Blindness and Camouflage | journal=Nature | year=1940 | volume=146 | issue=3694 | page=226 | bibcode=1940Natur.146Q.226. | s2cid=4071103 | doi-access=free }}</ref>

Some tentative evidence finds that the color blind are better at penetrating certain color camouflages. Such findings may give an evolutionary reason for the high rate of red–green color blindness.<ref name=Morgan>{{cite journal | vauthors = Morgan MJ, Adam A, Mollon JD | s2cid = 35694740 | title = Dichromats detect colour-camouflaged objects that are not detected by trichromats | journal = Proceedings. Biological Sciences | volume = 248 | issue = 1323 | pages = 291–5 | date = June 1992 | pmid = 1354367 | doi = 10.1098/rspb.1992.0074 | bibcode = 1992RSPSB.248..291M }}</ref> There is also a study suggesting that people with some types of color blindness can distinguish colors that people with normal color vision are not able to distinguish.<ref name = dimension/> In World War II, color blind observers were used to penetrate camouflage.<ref>{{cite news|title=Colour blindness not all it seems|url=http://news.bbc.co.uk/2/hi/health/4498734.stm|access-date=21 June 2016|work=[[BBC News]]|date=6 December 2015|url-status=live|archive-url=https://web.archive.org/web/20160623215610/http://news.bbc.co.uk/2/hi/health/4498734.stm|archive-date=23 June 2016}}</ref>{{Failed verification|date=October 2024}}

In the presence of chromatic noise, the color blind are more capable of seeing a luminous signal, as long as the chromatic noise appears [[Metamerism (color)|metameric]] to them.<ref>{{cite journal |last1=Sousa |first1=Bruna Rafaela Silva |last2=Loureiro |first2=Terezinha Medeiros Gonçalves |last3=Goulart |first3=Paulo Roney Kilpp |last4=Cortes |first4=Maria Izabel Tentes |last5=Costa |first5=Marcelo Fernandes |last6=Bonci |first6=Daniela Maria Oliveira |last7=Baran |first7=Luiz Claudio Portnoi |last8=Hauzman |first8=Einat |last9=Ventura |first9=Dora Fix |last10=Miquilini |first10=Leticia |last11=Souza |first11=Givago Silva |title=Specificity of the chromatic noise influence on the luminance contrast discrimination to the color vision phenotype |journal=Scientific Reports |date=21 October 2020 |volume=10 |issue=1 |pages=17897 |doi=10.1038/s41598-020-74875-3|pmid=33087826 |pmc=7578001 |bibcode=2020NatSR..1017897S }}</ref> This is the effect behind most "reverse" [[Pseudoisochromatic plate]]s (e.g. ''"hidden digit"'' [[Ishihara plate]]s) that are discernible to the color blind but unreadable to people with typical color vision.{{citation needed|date=September 2022}}

===Digital design===
{{See also|Color coding in data visualization}}
[[File:Safe Chart Colors-F99-FEC-ADD.jpg|thumb|alt=snippet of colored cells in a table (foreground), surrounded in background showing how the image appears in color-blindness simulations.|Testing the colors of a web chart, ''(center)'', to ensure that no information is lost to the various forms of color blindness]]
[[Color code]]s are useful tools for designers to convey information. The interpretation of this information requires users to perform a variety of [[#Color tasks|color tasks]], usually comparative but also sometimes connotative or denotative. However, these tasks are often problematic for the color blind when design of the color code has not followed best practices for accessibility.<ref>{{Cite journal |last=Hovis |first=Jeffery K. |date=July 2002 |title=Diagnosis of Defective Colour Vision, 2nd Ed. |journal=Optometry and Vision Science |language=en-US |volume=79 |issue=7 |pages=406 |doi=10.1097/00006324-200207000-00005 |issn=1538-9235 |doi-access=free }}</ref> For example, one of the most ubiquitous [[#Color tasks|connotative]] color codes is the "red means bad and green means good" or similar systems, based on the classic [[#Signal lights|signal light colors]]. However, this color coding will almost always be [[#Confusion colors|undifferentiable]] to [[#Deutan|deutans]] or [[#Protan|protans]], and can instead be supplemented with a parallel connotative system ([[Check mark|symbols]], [[smiley]]s, etc.).

Good practices to ensure design is accessible to the color blind include:
* When possible (e.g. in simple video games or apps), allowing the user to choose their own colors is the '''most''' inclusive design practice.
* Using other signals that are parallel to the color coding, such as patterns, shapes, size or order.<ref>{{cite book|last1=Caprette|first1=Heather|title=Best Practices in Accessible Online Design|publisher=Pressbooks @ MSL|chapter=14 Avoiding the Use of Color Alone to Convey Meaning and Algorithms That Help|chapter-url=https://pressbooks.ulib.csuohio.edu/accessibility/chapter/chapter-2-3-avoiding-the-use-of-color-alone-to-convey-meaning-and-algorithms-that-help/|access-date=12 August 2022|archive-date=12 August 2022|archive-url=https://web.archive.org/web/20220812064823/https://pressbooks.ulib.csuohio.edu/accessibility/chapter/chapter-2-3-avoiding-the-use-of-color-alone-to-convey-meaning-and-algorithms-that-help/|url-status=live}}</ref> This not only helps the color blind, but also aids understanding by normally sighted people by providing them with multiple reinforcing cues.
* Using brightness contrast (different shades) in addition to color contrast (different hues)
* To achieve good contrast, conventional wisdom suggests [[Color coding in data visualization#Grayscale, an important tool for visualization of data|converting a (digital) design to grayscale]] to ensure there is sufficient brightness contrast between colors. However, this does not account for the [[Luminous efficiency function#Color blindness|different perceptions of brightness to different varieties of color blindness]], especially [[#Protan|protan]] CVD, [[#Tritan|tritan]] CVD and [[#Monochromacy|monochromacy]].
* Viewing the design through a '''CVD Simulator''' to ensure the information carried by color is still sufficiently conveyed. At a minimum, the design should be tested for [[#Deutan|deutan]] CVD, the most common kind of color blindness.
* Maximizing the area of colors (e.g. increase size, thickness or boldness of colored element) makes the color easier to identify. [[Color coding in data visualization#Symbol size affects color salience|Color contrast improves as the angle the color subtends on the retina increases]]. This applies to all types of color vision.
* Maximizing brightness (value) and saturation (chroma) of the colors to maximize color contrast.
* Converting connotative tasks to comparative tasks by including a [[Chart#Features|legend]], even when the meaning is considered obvious (e.g. [[Red#Warning and danger|red means danger]]).
* Avoiding denotative color tasks ([[Color term|color naming]]) when possible. Some denotative tasks can be converted to comparative tasks by depicting the actual color whenever the color name is mentioned; for example, colored typography in "{{font color|purple|'''purple'''}}", {{color box|Purple|purple}} or "purple ({{Color sample|purple}})". 
* For denotative tasks ([[Color term|color naming]]), using the most common shades of colors. For example, green and yellow are colors of confusion in red–green CVD, but it is not common to mix forest green ({{Color sample|green}}) with bright yellow ({{Color sample|yellow}}). Mistakes by the color blind increase drastically when uncommon shades are used, e.g. neon green ({{Color sample|#0F5}}) with dark yellow ({{Color sample|#882}}).
* For denotative tasks, using colors that are classically associated with a color name. For example, using "firetruck" red ({{Color sample|red}}) instead of [[Burgundy (color)|burgundy]] ({{Color sample|#802}}) to represent the word "[[red]]".

===Color selection in design===
[[File:Delivery track of the board game Great Western Trail.jpg|thumb|Colors of [[board game]] pieces must be carefully chosen to be accessible to the color blind.]]
A common task for designers is to select a subset of colors (''qualitative'' colormap) that are as mutually differentiable as possible ([[Color coding in data visualization#Choosing salient colors for color coding|salient]]). For example, player pieces in a [[board game]] should be as different as possible.

Classic advice suggests using [[Cynthia Brewer#Brewer palettes|Brewer palettes]],{{citation needed|date=December 2024}} but several of these are not actually accessible to the color blind.{{which|date=December 2024}}

An issue with color selection is that the colors with the greatest [[Contrast (vision)|contrast]] to the [[#Red–green color blindness|red–green color blind]] tend to be [[#Confusion colors|colors of confusion]] to the [[#Blue–yellow color blindness|blue–yellow color blind]] and vice versa.

In 2018, [[user experience|UX]] designer Allie Ofisher published 3 color palettes with 6 colors each, distinguishable for all variants of color blindness.<ref>{{cite web|url=https://medium.com/@allieofisher/inclusive-color-palettes-for-the-web-bbfe8cf2410e|title=Inclusive Color Palettes for the Web|author=Allie Ofisher|website=Medium|date=18 May 2018|access-date=17 Dec 2024}}</ref>{{Self-published inline|date=December 2024}}

===Sequential colormaps===
[[File:CVD-friendly sequential colormaps.png|thumb|Three sequential colormaps that have been designed to be accessible to the color blind]]

A common task for data visualization is to represent a color scale, or ''sequential'' colormap, often in the form of a [[heat map]] or [[choropleth]]. Several scales are designed with special consideration for the color blind and are widespread in academia, including Cividis,<ref name=VIRIDIS/> Viridis<ref name="VIRIDIS">{{cite journal |last1=Nuñez |first1=JR |date=2018 |title=Optimizing colormaps with consideration for color vision deficiency to enable accurate interpretation of scientific data |journal=PLOS ONE |volume=13 |issue=7 |pages=e0199239 |doi=10.1371/journal.pone.0199239 |pmid=30067751 |pmc=6070163 |arxiv=1712.01662 |bibcode=2018PLoSO..1399239N |access-date=|doi-access=free }}</ref> and [[Parula#In data visualization|Parula]]. These comprise a light-to-dark scale superimposed on a yellow-to-blue scale, making them [[monotonic]] and perceptually uniform to all forms of color vision.