Color alone should never be used to convey information in a document. Users with visual impairments such as color blindness or color contrast deficiencies may not understand the content being presented, as they may not be able to distinguish between colors. Additionally, documents created with information based on color lose that information when printed on a black and white printer.
Do not use color alone to convey information in a document. Instead, supplement color with a visual element - such as an underline - or use headings to identify sections. If using color in charts, supplement color coding with texture, differences in line style, text in graphs, or shades of one color to improve accessibility. Charts should be readable in black and white.
Using Color in Text
Use headers or formatting elements such as underlines, borders, or other symbols along with color to convey meaning. Printing a color document in black and white is the best test to see if you have lost any meaning.
In the example below, the essential information (which assignments are required) is relayed using color only; the information is lost when printed in black and white. The simple addition of the asterisk symbol allows the document to maintain meaning when in black and white.
Using Color in Charts
In the example below, the top chart shows how the use of color alone renders a chart unusable. The lines in the graph are all the same style - solid. Although the lines are different colors, when the chart is displayed in black and white (or printed in black and white), you can no longer distinguish which line is associated with which value. The bottom chart uses lines that are different styles - solid, short dashed, and long dashed; when this chart is displayed in black and white (or printed in black and white), you can still distinguish which line is associated with which value.