Web Content Accessibility Guidelines (WCAG) 2.0

Web Content Accessibility Guidelines (WCAG) 2.0 covers a wide range of recommendations for making Web content more accessible. These guidelines will also often make your web content more usable to users in general.

Principles of Accessibility

Anyone who wants to use the Web must have content that is:

• Perceivable-Information and user interface components must be presentable in ways they can be perceived.

• Operable - User interface components and navigation must be operable.

• Understandable - Information and the operation of user interface must be understandable.

• Robust - Content must be robust that it can be interpreted reliably by a wide variety of user agents and assistive technologies.

Guidelines for making content perceivable

• Provide text alternatives for non-text content – like braille, speech etc.

• Provide alternatives for time-based media.

• Create content that can be presented in different ways.

• Make it easier to see and hear content separating foreground from background.

Color Text Legitibility

W3C Guidelines for color readability

The brightness difference between foreground text-color and background-color should follow the formulae suggested in W3C Guidelines for good text-color visibility.

Color visibility algorithm (suggested by W3C standard)

Two colors provide good color visibility if the brightness difference and the color difference between the two colors are greater than a set range.

 

Color brightness =  ((Red value X 299) + (Green value X 587) + (Blue value X 114)) / 1000    For  good color visibility  brightness difference  should  be  >  125

 

Color difference =      (maximum (Red value 1, Red value 2) - minimum (Red value 1, Red value 2)) +    (maximum (Green value 1, Green value 2) - minimum (Green value 1, Green value 2)) +    (maximum (Blue value 1, Blue value 2) - minimum (Blue value 1, Blue value 2)) For  good color visibility  color difference  should  be  >  500

 

Note:

These formulae are only suggestions and are not reliable to full extent. In actual practice you are expected to test the color combinations again and again for readability.