This Developer Tools extension allows you determine whether or not the color contrast on a site is WCAG 2.0 AA and AAA compliant.
ColorA11y allows you to easily select a foreground color and a background color, and determine whether or not the contrast ratio between the 2 colors is WCAG 2.0 compliant. ColorA11y can help validate the existence of web accessibility issues you think you already have with color contrast. This Developer Tools extension can also help verify you're technically adhering to the WCAG 2.0 color contrast guidelines. Simply open the Developer Tools in Chrome, and open the ColorA11y tab. Currently, this works best using Mac's color picker, and not the Windows native tool. I'm working on integrating this with Spectrum, and will have an update shortly.