- hihayk.github.io/scale/ allows to take a hex color and create lighter and darker colors with a beautiful and focused user interface. It does not indicate WCAG contrast. The tool is part of hayk.design. ❤️
- Theme Machine by Keith J. Grant is a combination of a color picker and a palette builder. It's quick and comfortable. Keith has written an article on his blog: Theme Machine: A CSS Color Palette Tool.
- leonardocolor.io allows to define color palettes and indicates WCAG contrast.
- huetone.ardov.me has sample palettes of Stripe, Chakra, IBM, GitHub and the like.
- github.com/primer/prism/ is an experimental GitHub tool for defining accessible color palettes to be used for light mode and dark mode. See the blog post Accelerating GitHub theme creation with color tooling.
- convertacolor.com, by Tim Bennetto. Convert colors between formats HEX, RGB, HSL and CMYK.