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.
For more readable presentations, Web pages and
• 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
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
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:
For usability testing, see: