Color Deficient Vision

Simulation in the Web Designer's Color Card and Chart

Color Card
The VisiBone Web Designer's Color CARD
(8.5" x 11")
Color Chart
The VisiBone Web Designer's Color CHART
(18" x 24")
Printed color
references with
color deficiency

deutanmini.jpg (6232 bytes)Toward the lower left on the Card and the Chart is a simulation of deuteranopia, a common variety of color blindness.

This is from the Greek for "second doesn't see" referring to the second cones in the retina of the eye that respond primarily to green light and are presumed to be defective in this condition.

This doesn't mean that greens are invisible to people with deuteranopia. Human vision is complicated.

The role of the green cones is less to detect green light than to distinguish it from red.  Similarly, when the red cones "don't see" (protanopia), the main consequence is that reds, yellows and greens are indistinguishable.

deutanfigure.jpg (16268 bytes) This figure simulates the web-safe colors as they appear in a deuteranopic condition.  In most other categories of color blindness, protanopia, protoanomaly and deuteranomaly, the view is very similar but there are subtle differences.  In one very rare form, called tritanopia, affecting thirty people in a million, colors appear very differently.  The Color-deficient vision site excels at explaining and illustrating these points.

cardgrid.gif (30127 bytes)Here is the main web-safe color reference in the Card and the Chart.

In most forms of color blindness, these colors appear similar to those above.  When designing a web site, you might try to avoid depending on distinctions that color-blind people cannot make.  About 8% of men and 0.4% of women have some form of color blindness.

Background A color scheme designed to be distinguished in color blindness Christine Rigden formerly of has a very informative public service site, Safe Web Colours for Colour Deficient Vision.  The chart on the right shows a color scheme with a simulation of how it would look in two different types of color blindness.  The colors were chosen to be certain anyone could tell them apart.
Human-Computer Interaction Resource Network
Thomas Wolfmaier runs the Human-Computer Interaction Resources Network, a repository of wisdom in the quest for humans and computers to get along much better than they do.  Some content is under subscription but there's a big searchable collection of books, periodicals and other resources.
See any web page as color blind users see it
Vischeck has a terrifically practical service. Forget all the theory, just see what your site looks like to color blind users. It will simulate the appearance of an entire web page in various forms of color blindness. (Select the Deuteranope option for the most common.) It can't convert the colors of certain objects, but it does a great job on most features. Highly recommended.

Tests For Color Blindness

The following sites may be helpful if you suspect you have color vision deficiency.  They are not meant to be diagnostic.  See your vision care professional.

Normal color vision should see a "5" more than a "2"Ishihara Test for Color Blindness, by Dr. Shinobu Ishihara.  This has several online tests.

Color Vision Testing Made Easy, by Dr. Terrace Waggoner, distributed by Bernell.   This site seems very useful, testing step by step.

Professor Holmgren’s Test For Color Blindness  This test uses colored wools.