WCAG 2.0 is divided into three conformance levels (A-AA-AAA) because the success criteria are organised based on the impact they have on design or visual presentation of the pages. The higher the level, the more restraining it becomes on design.

WCAG is separated into three conformance levels:

1. Level A – some impact on design

2. Level AA – medium impact on design

3. Level AAA – high / extreme impact on design

For example, let's take guideline 1.4 (Distinguishable), which is about making it easier for users to see and hear content including separating foreground from background.

• Success Criterion 1.4.1 is about the Use of Color. The rule goes like this: Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element. (Level A)
• Success Criterion 1.4.3 is about Contrast (Minimum). The rule goes like this: The visual presentation of text and images of text has a contrast ratio of at least 4.5:1, except for the following: (Level AA)
• And finally, success criterion 1.4.6 is about Contrast (Enhanced). And the rule goes like this: The visual presentation of text and images of text has a contrast ratio of at least 7:1, except for the following: (Level AAA)

"Note 2: It is not recommended that Level AAA conformance be required as a general policy for entire sites because it is not possible to satisfy all Level AAA Success Criteria for some content.

AA compliance, the most common, requires a minimum contrast ratio of 4.5 or 3 for large text, while AAA compliance, the more stringent or rare, requires a minimum contrast ratio of 7 or 4.5 for large text. Large text for AA and AAA is 18.66px minimum.

Provide enough colour contrast.

The success criteria: “Ensure your website has enough colour contrast. It helps people who are colour blind, have low vision or are legally blind, but the right contrast in colour is visually appealing for all people.”

Despite a few exceptions, the practical application of contrast means “the visual presentation of text and images of text has a contrast ratio of at least 4.5:1”.

The example above demonstrates the same text contrasted differently. Text colour can significantly affect readability, depending on the chosen background colour.