tota11y - An accessibility visualization toolkit from Khan Academy
Coolors.co - The super fast color schemes generator! Create, save and share perfect palettes in seconds!
Nibbler - Free tool for testing how good your website is, and what you can do to improve it. Check accessibility, SEO, social media, compliance and more.
Polarite.app - A.I. assisted color scheme generator
Page Speaker - Modern web accessibility tools for agencies & webmasters
Rainglow Color Themes - 320+ color themes for a variety of editors and software.