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 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.

To provide alternative color schemes for color blind users, you can specify color combinations through cascading style sheets (CSS). The cascading feature makes it possible to combine different CSS files.

For example, you can use a combination of:

You can select the CSS file that specifies colors from three variants:

For dashboard diagrams, you can have different versions of symbol palettes and select the appropriate version.