Definitions of the different types of colour blindness – summary
Trichromatic vision – normal colour vision, all three cone types function normally. A person with normal colour vision is known as a trichromat.
Anomalous trichromacy – a milder form of colour vision deficiency where one type of cone cell does not function normally, affecting ability to perceive many colours.
Dichromacy – a severe form of colour vision deficiency where one cone type is missing. A dichromat is a person who has dichromacy, i.e. protanopia, deuteranopia or tritanopia
- Protanopia and protanomaly: relate to a red vision deficiency.
- Protanopia is a severe condition, where no cones to absorb red light (red cones) exist
- Protanomaly is a less severe condition, where red cones exist but don’t function normally.
- Deuteranopia and deuteranomaly: relates to a green vision deficiency.
- Deuteranopia is a severe condition, where no cones to absornb green light (green cones) exist;
- Deuteranomaly is a less severe condition, where green cones exist but don’t function normally.
- Tritanopia and tritanomaly: relates to a blue vision deficiency.
- Tritanopia is a severe condition, where no cones to absorb blue light (blue cones) exist;
- Tritanomaly is a less severe condition, where blue vision cones exist but don’t function normaly.
Monochromacy – the most severe form of colour vision deficiency where no colour is perceived. Monochromats have monochromatic or greyscale vision and often have other vision issues such as achromatopsia (see Resources).
AA rating – the minimum colour contrast ratio to be applied between two colours to ensure accessibility for people with CVD. See WCAG 2.1 below. WCAG 2.1 has three ratings standards – A, AA and AAA. The AA rating ensures sufficient colour contrast for all types of CVD and caters to 20/40 vision, i.e. for those with visual impairments who do not use assistive technology.
For text of 18pt or smaller the minimum colour contrast ratio for AA rating is 4.5:1.
For text larger than 18pt the minimum colour contrast ratio for AA rating is 3:1
The AAA rating is more onerous and stipulates a minimum colour contrast ratio of 7:1. This ratio is recommended for all body text.
Colour contrast ratios can be calculated easily using a variety of free, downloadable software packages to suit individual needs. See Resources.
When building AA compliant websites, it is important to understand the different between web built and images used on the website. Websites built to meet AA will have guidelines for HTML pages to ensure the colour and the boldness of the font versus the background will meet a specific contrast ratio. There are several tools online that will help in calculating colour contrast ratios such as https://webaim.org/resources/contrastchecker/. However, images loaded into a webpage can bypass these checks, therefore all designs and images used as diagrams will need to be manually checked before loading into a website.
In addition, ensuring the colour contrast ratio described above unfortunately will not solve the challenge of differentiating between two colours. This requires additional checks to ensure it is clear through the use of secondary labelling techniques – e.g. icons/texture/text – which areas are represented by different colours. The secondary labels must always also be mirrored in the key at a scale which will be legible.
Colour blindness – a colloquial term for Colour Vision Deficiency (CVD)
Colour contrast ratio – the difference in colour contrast between two colours. This is usually calculated during the design process using bespoke software to check accessibility requirements are met. Minimum colour contrast ratios for colour blindness accessibility are specified in accordance with World Wide Web Consortium (W3C) Guidelines: https://www.w3.org/TR/WCAG21/ (check for later versions, these are constantly updated).
Colour vision screening – testing a person’s vision to ascertain if they have a colour vision deficiency, normally undertaken using the Ishihara test.
Cones – specialised nerve cells (photoreceptors) within the retina at the back of the eye. There are three types of cone cells in humans which respond differently to different light wavelengths, absorbing red, blue and green light respectively. The cone cells work together and are responsible for colour vision.
Coping strategy – the behavioural and cognitive efforts made by individuals in attempting to deal with stressful situations.
Colour vision deficiency (CVD) – generally an inherited condition which creates an abnormality, or deficiency, of any of the types of cone cells and results in abnormal colour vision (the inability to perceive colours normally). There are three basic variants of colour blindness depending upon which cone cells are affected – protan, deutan and tritan deficiencies. Milder forms of colour blindness are known as anomalous trichromacy, where all the cone types work but one type does not function normally. Dichromacy is a severe form of colour vision deficiency where one cone type doesn’t function at all.
Deuteranopia – a severe form of colour vision deficiency, dichromacy, where there are no functioning cone cells to absorb green light.
Deuteranomaly – a form of anomalous trichromacy where cone cells which should absorb green light don’t function normally.
Disability – The social model of disability says that disability is created by physical, sensory, intellectual, psychological and attitudinal barriers. The social model identifies solutions to remove or reduce these barriers within society, rather than trying to fix an individual’s impairment or health condition. The social model is the preferred model for disabled people. It empowers disabled people and encourages society to be more inclusive. For the purposes of disability legislation, it is widely accepted that a person has a disability if he or she has a physical or mental impairment that has a substantial and long-term effect on his or her ability to carry out normal day-to-day activities affecting one or more of several categories including ‘speech, hearing or eyesight’. It is important to remember that colour blind people face hidden barriers and can be considered to have a disability.
Hue – a colour’s property, e.g. red, orange, yellow, blue.
Indirect sexual discrimination – it is indirect sex discrimination to have a rule, policy or practice which someone of a particular sex is less likely to be able to meet; thereby placing them at a disadvantage to the opposite sex. This can sometimes include colour vision deficiencies where colour blind males may be disadvantaged in certain situations compared with females, such as at work.
Ishihara test – a simple screening test to establish whether a person has a form of red or green colour vision deficiency. https://en.wikipedia.org/wiki/Ishihara_test.
Minimum colour contrast ratio – the minimum recommended contrast ratio between two colours to meet the requirements of WCAG 2.1 (or later versions). The minimum ratio varies depending upon the rating level being applied. There are different minimum colour contrast ratios for different rating levels depending upon the size of font, etc. For more information see WCAG 2.1. To ensure accessibility for people with colour blindness the minimum colour contrast ratio must never be less than 3:1.
Protanopia – a severe form of colour vision deficiency, dichromacy, where there are no functioning cone cells to absorb red light. Due to the lack of cone cells absorbing red light someone with protanopia will have a shortened visible spectrum and will perceive many reds as black.
‘Red/green’ colour blindness – a misnomer. It is a common misconception that all people with colour blindness have ‘red/green’ colour blindness and confuse only reds and greens. This may be because people with protan and deutan types of colour blindness most commonly experience problems distinguishing between reds and greens. However, red/green colour blindness is not a specific condition, it is a term which encompasses mild to severe forms of both protan and deutan deficiencies. People with protan and deutan deficiencies don’t just experience problems distinguishing between reds and greens, many colour combinations can be confused.
Safe colour palette – a misnomer. A safe colour palette would be a suite of colours within which everyone with colour blindness could distinguish between all colours used. This may be achievable only in very limited circumstances involving probably no more than three colours in addition to black and white. This is due to the need for minimum colour contrast ratios of at least 3:1 to be achieved between all colours.
Tritanopia – a severe form of colour vision deficiency, dichromacy, where there are no functioning cone cells to absorb blue light. A person with tritanopia will experience difficulties distinguishing between blues and yellows in particular.
WCAG 2.1 – The International Accessibility Standards were updated in August 2018 to version WCAG 2.1 (see References) and have three ratings standards – A, AA and AAA. AAA is the most onerous and AA is the minimum standard which must be met to ensure people with colour blindness can fully access information. WCAG 2.1 is equivalent to European Standard ETSI EN 301 549 and is also incorporated into the UK The Public Sector Bodies (Websites and Mobile Applications) Accessibility Regulations 2018 http://www.legislation.gov.uk/uksi/2018/852/contents/. Check https://www.w3.org/ for the latest updates of WCAG. At the time of publishing this guide, WCAG 2.2 is currently under development.
Further Guidance and Resources
World Rugby resources
Colour Blind Awareness – www.colourblindawareness.org
Scottish Rugby Podcast – https://www.scottishrugby.org/fanzone/episode-6-of-the-scottish-rugby-official-podcast-released at 36-40mins
Finding Neymar: The role of colour in the detection and discrimination of football kits – Burnell and Thompson (2021) https://journals.sagepub.com/doi/10.1177/03010066211019370
Sports Surfacing for the Colour Blind – GrassSports Australia https://www.colourblindawareness.org/wp-content/uploads/2019/11/Grassports_colour-blind-manual_FA_WEB.pdf
Stadium Safety, Security and Service
- St Denis (European) Convention on an Integrated Safety, Security and Service Approach at Football Matches and Other Sport Events (in particular Annexures A and C) https://www.coe.int/en/web/sport/recommendation-2015-1
- Sports Ground Safety Authority ‘Green’ Guide to Safety at Sports Grounds (Sixth Edition) https://sgsa.org.uk/greenguide/ in particular Appendix C https://sgsa.org.uk/wp-content/uploads/2019/02/Annex-C-Guidance-on-colour-vision-deficiency.pdf
- Colour Blind Awareness, see above (as auditors of stadiums on behalf of UEFA and contributors to the St Denis Convention and SGSA Green Guide Annexures)
- 15 Steps to Create Accessible and Inclusive Ticketing Processes - Centre for Access to Football in Europe https://www.cafefootball.eu/Handlers/Download.ashx?IDMF=b4595b9d-c57b-4a8a-bf15-afdf6bd209a0
Creating accessible designs
Web Content Accessibility Guidelines WCAG 2.1 https://www.w3.org/TR/WCAG21/
Software resources for calculating colour contrast ratios
Advice on creating accessible presentations
World Rugby takes no responsibility for any software listed in this document. Any software is listed in this document is downloaded at the users’ risk.
Throughout this document where images are in pairs, 'colour-blind' simulated images are shown alongside. Unless otherwise stated, these illustrative images mostly indicate severe red or green types of colour blindness and have been selected to demonstrate the specific points made within the text and according to the context of the original. No simulation software can be relied upon to be an accurate representation of the type of colour vision deficiency experienced by an individual with colour vision deficiency. For specific advice to support people with blue/yellow deficiencies or monochromacy, please contact Colour Blind Awareness directly (firstname.lastname@example.org).