December 10, 2004  
 

 

Color Vision Deficiency Can Change the Way You View Things

By Raven Hanna

Graphics software like PowerPoint places the spectrum of color at your command with an easy click of the mouse. You should be aware, however, that some color combinations can make information completely unreadable to people who perceive color differently.

Presentation Tips

For more readable presentations, Web pages and graphics:

  • Use a dark font on a light background

  • Use color sparingly

  • Use saturated colors rather than pale colors

  • Avoid red and green

  • Check if there is enough shade differentiation by printing in grayscale

  • Check what the colors would look like to the color-deficient using an on-line translator

  • Use redundancy for color information, e.g. use patterns as well as color to distinguish lines in graphs

  • Use fonts large enough to reach your audience in the venue (big room, big fonts)

 

Color vision deficiency—known by the misnomer color blindness—is more common than you may think. Many people do not realize they perceive the world differently until well into adulthood. An estimated one out of 12 men and one out of 125 women are affected. Based on these figures, statistically there would be over 100 people at SLAC with color deficiency.

Altered Sensitivity to Wavelengths

Color deficiencies are caused by the reduced or altered sensitivity to certain wavelengths of light by cone cells in the eye. Each of the three flavors of cone cells perceives a different color of light: red, green or blue. The full range of hues we see are a mixture of these three colors.

The genes for cone cells are located on the X-chromosome, which explains why color deficiencies are more common in men. If a male inherits an X-chromosome with a color-deficient trait, he does not have a second X-chromosome to make up for the deficiency, while females do.

Deficiencies in different types of cone cells lead to different types of color perception. Out of 1,000 males, about 33 are weak in green perception (called deuteranomalous), 8 perceive no red (protoanopia), 6 perceive no green (deuternopia), and 5 are weak in red (protanomalous). Diminished blue perception is rare because rod cells also detect blue light and can make up for blue cone deficiency.

Clues for Clear Communication

Paying attention to color usage is especially important in preparing presentations, on signage and on the Web. A general rule of thumb to ensure text readability is to use a dark colored font on a light background. Try viewing the slide, graphic or figure in grayscale to check if the colors can be differentiated by shade alone. It is best to use color sparingly and as a highlight, because essential information may be lost to your viewers.

Be especially careful when using red and green. Depending on the type of color deficiency, red can look black (red-insensitive) or yellow (green-insensitive), making it unclear when used with either a light or a dark background. Websites are available to check your slides and Web pages for readability by the color deficient audience members.

These guidelines are also applicable to duplicating and video recording. Multimedia supervisor Herb McIntye (PAO) suggests using dark color text on light backgrounds because of the sensitivity of the camera. Yellow lettering is particularly difficult to see and should be avoided.

The SLAC Medical Department checks for color deficiencies using the Ishihara Test, which shows a field of dots differentiated into numbers using color. Other, more extensive, tests include color pencil matching and distinguishing color patches.

For more information on color deficiencies, see: http://members.shaw.ca/hidden-talents/vision/color/colorblind1.html and http://webexhibits.org/causesofcolor/2.html

For usability testing, see: http://www.vischeck.com/vischeck/ or http://colorfilter.wickline.org/ 

 

 

The Stanford Linear Accelerator Center is managed by Stanford University for the US Department of Energy

Last update Thursday December 09, 2004 by Emily Ball