Design for Disability Access.
Colour Vision Impairment.
There are many types of colour blindness. A brief and very simplified description is included to demonstrate that certain elements must
be present in order for a website to be fully accessible to all users.
References to in-depth descriptions at the end of this page.
Main principle we apply to our Accessibility
Web Designs.
We do not rely on colour alone to convey information.
Approximately 8% of (Caucasian) males and 0.5% of females exhibit some form of color vision deficiency. That translates in to 1 in
every 20 web site visitors.
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Coloured text on a coloured background may be illegible.
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Images may be unrecognizable
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Links that are not clearly marked as links may be unrecognizable.
Examples:
This is not a clearly defined link:
Home
Page.
This is a clearly defined link: Home Page.
Types of Colour Vision Deficiencies:
Trichromatic: Regular vision. The person sees using all three primary colours and
mixes thereof.
Anomalous trichromat - Is able to see and mix all primary colours, but
their perception is different from regular tricomats.
Protanomaly: reduced red sensitivity.
Deuteranomaly: reduced green sensitivity.
Tritanomaly: reduced blue sensitivity.
Dichromat - can mix only two visual pigments. This can vary greatly with
red, green or blue is missing.
Protanopia: unable to receive red:
Deuteranopia: unable to receive green:
Tritanopia: unable to receive blue.
Monochromat (Achromatopsia) - People with Monochromatic vision see only one color, ergo sees no colour and are unable to mix colours.
Typical Monochromatic: unable to combine colors.
Fully grayscale. Also known as Rod Monochromat.
Atypical Monochromatic or Cone Monochromatic: very low color recognition.
Design Problems and Solutions.
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selecting color combinations that can be discriminated by individuals with
different types of color vision deficiencies. See what a colour blind person
might see on a web page, by combining background and text colours here:
[opens new window] Color
Vision by Cal Henderson.
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Contrasting background to foreground
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When color coding, always provide redundant cues, such as texture, line
shading, location, and explicit labels.
Example of poor colour combinations:
A pink (light red)
background with Green Text...
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...might
look like this to some forms of colour blinds.
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A better Choice
might be a slightly tinted background with a strong contrast foreground.
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Test your colour vision here:
[opens new window] The UMIST 'For Fun' Colour Vision Test:
An online test for color vision deficiencies.
Design for Poor or No Hand
Movement -
Design for Sight Impairment - Design for Colour Vision Impairment -
Design for Dyslexia - Design for Hearing Impairment
- Design for Epilepsy - Design for Cognitive Impairment.
- Tips and Hints
Disclaimer.
End of document.
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