This Color Contrast Analyzer is a tool to help you identify good color combinations from an accessibility standpoint. The color visibility in this tool is calculated based on suggested algorithms from the World Wide Web Consortium (w3)

The Color Contrast Analyzer will calculate the visibility based on the Web Content Accessibility Guidelines as recommended by the w3. There are two versions of the guidelines, version 1.0 which was presented in 1999, and Version 2.0 which is still a working draft.

The w3 recommendations define three levels of conformance to their guidelines. Priority 1, 2 and 3. Their 2.0 color contrast algorithms utilizes two of these-- Priority 2 (AA), and Priority 3 (AAA). Whether or not you need to reach an AAA conformance depends on your target audience. Read more about this on the w3 site. For large text (over 18 points) the contrast ratio for AA is 3:1 and for AAA 5:1. For small text it's 5:1 for AA and 7:1 for AAA.