CUD helps ensure that graphical information is conveyed accurately to people with various types of color vision impairment, including people with color blindness. Several countries have guidelines that require CUD-compliant graphics in public spaces.
The most common types of color blindness are protanopia (blindness to red) and deuteranopia (blindness to green). About one-third of color blind people are completely blind to red or green; most of the remainder have milder forms of color blindness.
In the figure below, the color wheel labeled A is the original image. The color wheel labeled B is a proof of how an individual with protanopia sees the original. The color wheel labeled C indicates a color combination that is perceivable to the greatest number of individuals.