Contrast
Contrast makes it easy to check the contrast ratios of colors as you work. Select a layer and Contrast will immediately look for the color directly behind your selection and serve up the contrast ratio along with passing and failing levels from the Web Content Accessibility Guidelines (WCAG).
You may like
Validate your Web Site with A11ygator.
A GUI desktop app to find Accessibility problems in webpages. Tool for Web Developers.
Learn digital accessibility from scratch with comprehensive WCAG guidelines, practical tutorials, and expert tools.
Solve accessibility issues before they reach your customers.
Expanding the potential of the web for people with disabilities by empowering individuals and organizations to create accessible content.
The introduction on web accessibility that I want to give every single web developer.