When color is used to convey information, the same information should be available in a form that does not depend on the ability to perceive color.
Color is an important asset in Web design, enhancing usability and aesthetic appeal. However, some users have difficulty perceiving color. People with partial sight often experience limited color vision, and many older users do not see color well. In addition, people using text-only and monochrome displays will be unable to access information that is presented only in color. The solution is to include the information in the source document while setting presentation properties in a style sheet.
Make image structure available to the sense of touch
Editorial Note: Not exactly sure where to map this technique?
Visual images may be converted into tactile form. For example, images can be printed as detailed reliefs using a specialized adaptation of Braille. Alternatively, the images can be printed on special paper and converted into raised-line drawings (as in the example from the Tate Gallery's IMAP project discussed in the technique on using alternative views to show the structure of complex images). These relief drawings can also be used as overlays on a digitizing tablet. With the aid of additional software, the image becomes a "touch screen" and provide spoken output as the user presses different areas.
The University of North Carolina's BATS project produces maps that use both tactile and auditory cues to provide information about locations and the distances between them. See Mark Tosczak "A New Way to Read, Not See, Maps." Wired News September 25, 2002. Available at http://www.wired.com/news/school/0,1383,54916,00.html. Accessed August 26, 2004.
Liddy Nevile's "Accessible Diagrams" page (2002) provides a useful overview of techniques and technologies for producing tactile graphics, both on- and off-line. Available at http://www.latrobe.edu.au/webaccess/diagrams.html.
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Example 1. A form has both required and optional fields. Required items are marked with an asterisk and shown in red. The asterisk is included in the label text and the color is specified in the style sheet.
Example 2. An examination. Students view an SVG image of a chemical compound and identify the chemical elements present based on the colors used in the diagram. The text alternatives associated with each element name the color of the element and indicate the element's position in the diagram. Students who cannot perceive color have the same information about the compound as their classmates. (This technique also satisfies Guideline 1.1 Level 1.)