Colorblindness in the
Classroom:
A Resource for Faculty
and Students
Daniel
Graham, Ph.D.
Department of Psychology
Hobart and William Smith Colleges
Colorblindness
is the most common sensory deficit one is likely to encounter in the classroom.
This guide provides a brief introduction to the neuroscience of colorblindness
so that faculty and students can understand what is
experienced by people with this condition. There are also tips on how
instructors can adapt their teaching materials, as well as tips for students
with colorblindness.
Colorblindness is a genetic condition that occurs in
around 8% of males and 0.5% of females, which affects light-sensitive neurons
in our eyes called cone photoreceptors. Most people are born
with three varieties of cones, which are sensitive to blue, green, and red
light, respectively (see Figure 1); such individuals are called trichromats. People
with colorblindness are generally born with only two of these types of cones which makes them dichromats. However, dichromats usually have the same overall number of cones as
trichromats, so their visual acuity for greyscale images is generally as good as or better than
that of trichromats.
Legend:
S = Blue cone photoreceptor
M = Green cone photoreceptor
L = Red cone photoreceptor
R = Rod photoreceptor (used for
night vision)
Figure 1. Sensitivity of human photoreceptors to different wavelengths of
light.
The most common form of colorblindness is red/green colorblindness (occurring in ~2%
of males). In this condition, there will usually be only two kinds of cones in
the eye: blue and red cones, or blue
and green cones. Someone with this
condition will not be able to tell the difference between most red and green
colors (see Figure 2).
Figure 2: Appearance of colorful hats to a trichromat (left) and to a dichromat
with red/green colorblindness (right). Image courtesy
vischeck.com.
Many people with colorblindness learn shortcuts for
guessing how objects and colors appear to a trichromat
by using other visual information (brightness, subtle variations in hue,
orientation, etc.). However, because visual information is so pervasive, there
are many situations in daily life and in the classroom that present
challenges to dichromats.
TIPS FOR
INSTRUCTORS
á
Avoid color in slides entirely unless it is necessary.
o Colorful slides may be more attractive than black and
white slides but they risk making important information invisible to people
with colorblindness.
o Use a black font or line color on a white background
for maximum visibility.
á
Avoid green whiteboard markers
o Because both dichromats and
trichromats are most sensitive to green light, green
whiteboard markers will appear almost as bright as the background of the
whiteboard. For trichromats, the difference in color
makes it easy to see green marker despite the similarity in brightness compared
to the whiteboard. However, dichromats cannot see
this color difference: green marks will appear as a bright grey that is very
similar to the white of the whiteboard, so these marks will be essentially
invisible.
o Avoiding green also means there is less likely to be
confusion in whiteboard figures that include more than one color.
o Make black markers your default.
o The same points apply for SMARTboards.
á
Avoid red laser pointers.
o Around half of people with red/green colorblindness
are especially insensitive to red light. Because of this, most red laser
pointers will not appear brighter than the light coming from the projector
screen, and will therefore be essentially invisible.
o Blue light laser pointers are available online, and will
be much more visible to people with colorblindness.
o Higher-powered red pointers – those greater
than 1 milliwatt (1 mW) in
power may be visible to dichromats.
o Using a pointing stick instead will also eliminate
these issues.
á
Be prepared to describe in words any slide or drawing
in a way that does not depend on the colors.
o The website vischeck.com provides an
approximation of the way you're your slides, websites, and other images appear
to someone with colorblindness. Consider testing your slides, especially
diagrams that involve a lot of color coding of
information. There are other sites that purport to provide this service but
some are not accurate.
o Powerpoint can convert color images to black and white. In the
Format Picture menu, select Adjust Picture>Grayscale.
TIPS FOR STUDENTS
WITH COLORBLINDNESS
á
Let your instructors know about your condition (if
you feel comfortable telling them) at the beginning of the course.
o Also let them know if particular
images/slides/figures are hard for you to see.
á
Companies such as EnChroma and O2Amp produce
eyeglasses with color filters that make red/green distinctions more visible to you.
o These products will not cure colorblindness,
and they will not make the world appear any more colorful (despite some
manufacturer claims) but they will make it easier for you to see some color
distinctions that would otherwise be invisible to you.
á
Let your instructors know about this resource.
Please feel free to contact Prof. Graham with questions or for further information.