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Communication - Use of color
Use of Color
Appropriate use of color is fundamental for accessibility. WCAG 1.0 in guide number 2, states. Do not base choices exclusively on color. Make sure graphics tests are visible when seen without color. Note two following points:
2.1 Ensure that all information conveyed with color is also
available without color, for example from context or markup.
2.2 Ensure that foreground and background color combinations
provide sufficient contrast when viewed by someone having color
deficits or when viewed on a black and white screen.
The Italian Guidelines containing the technical requirements, the definitions of the different accessibility levels and the technical methodologies for the testing of Web site accessibility contains various criteria for the use of color.
The following algorithm - suggested by the W3C - can be used to calculate differences in brightness and color between text and background:
Note that the algorithm is merely a guideline as it takes into account only the RGB (Red, Green, Blue) characteristics, whereas each monitor has its own brightness settings.
You can easily test your pages using the following online tools
The most common type of color blindness is difficulty in distinguishing reds, and the second most common is in distinguishing greens. There are various types of color blindness:
Colorblind Web Page Filter <http://colorfilter.wickline.org/> is
an online program for testing pages for accessibility in various
types of color blindness.
Sample table of HTML colors with esadecimal values (italian