Color is a service of Adobe Creative Cloud that generates themes for use in Adobe desktop apps such as Photoshop and Illustrator, and Adobe mobile apps such as Illustrator Draw and Photoshop Sketch.
Color Contrast Checker is a free tool that you can use to test the contrast on your foreground and background colors. Developed by Mari Johannessen, you simply type in your color HEX codes and it gives you a color contrast ‘score’.
Color Oracle is a free color blindness simulator for Windows, Macs, and Linux that takes the guesswork out of designing for color blindness by showing you in real time what people with common color vision impairments will see.
A collection of repeatable SVG background patterns for you to use on your web projects. You can also download and move into your favorite editing program to use in your other projects such as slide decks or infographics.
Growing source of information about color theory, color perception, color vision, and color combinations. You can create custom color palettes and check against an example, as well as use their color vision deficiency tool to check for consistency with color blindness.
Toptal has a completely free, web-based color design tool called ColourCode. It is an all-in-one color design tool where you can find different palette categories (analogic, triad, quad, etc.), multiple conversion colors, and even download your custom palette.
App available through the iTunes store, this tool lets you visualize colors as they are perceived with various types of color blindness. Move the Sim Daltonism window over something on the screen and see what it looks like with a color blindness.