Accessible material design palettes with Color Tool
A classical tool, made by Google in 2014, to help you to build accessible color palette for your user interfaces and measure the accessibility of your own color combinations.
Color Review
Find, test & explore accessible colors. A pleasant and intuitive tool to help designers to build color palettes. Certainly the tool I use the most when I'm doing visual design.
Tanaguru contrast finder
A tool to help designers to find color combinations that provide the best color contrast ratio.