Five to ten percent of all people have a deficiency in
color vision known as “color blindness”. Most people
can see colors to some degree, but not all people see colors in the
same way. For example, people with Protan vision have difficulty seeing
red, people with Deutan vision have difficulty seeing green, and people
with Tritan vision have difficulty seeing blue. Avoid using certain
color combinations in critical applications, because not all people
can distinguish them. For such color blind users, you must use what
is known as “color picking”, which is the
deliberate avoidance of colors that color blind users are unable to
distinguish. Specifically, when you use a set of colors in a diagram
or chart, you should avoid using red and green in the same display
for red-green-blind users, but you can use a range of colors from
blue to yellow. The same applies to using blue and yellow in displays
for blue-yellow-blind users.
In accessible applications, the information that is presented
by using colors is also presented in other ways. The colors that are
used therefore become redundant and are known as “redundant
colors”. For example, the data presented in a diagram
or chart might be presented additionally as text in a table. Graphic
objects might be presented additionally as specific shapes, or with
alternative color schemes, so that colors are not the only way to
distinguish items.
You can find a sample that illustrates the accessibility
features of the JViews Framework in <installdir>/jviews-frameworkxx/samples/accessibility.