The Designer's Dictionary of Color by 
Best Practices for Graphic Designers, Color Works by Kuler — Adobe color palette resource
Coolors — interactive color palette generator
Randoma11y — accessibility-friendly random color generator for text & background combinations
Build accessible colour combinations
Free and open platform for color inspiration
Put two valid CSS color values, in the format you choose--hex, RGB, RGB%--then choose the number of midpoints you'd like between them and blend. You'll get intermediate colors with their hexadecimal codes.
Web Color Chart - Hexadecimal - by VisiBone
Bob Stein has arranged the 216 hexadecimal HTML color codes by hue and presents them as cards, charts and swatches, some free and some at cost.
provides a web-safe diagram, web-smart colours, named colours, 500+ colours, web-safe colours by hue, and colour links.
Color Theory
Color theory is the collection of rules and guidelines which designers use to communicate with users through appealing color schemes in visual interfaces.
Everything about color, usage, and designing with color
Library of color schemes. HTML and CSS color codes available.
Create the perfect palette or get inspired by thousands of beautiful color schemes. The super fast color schemes generator!
Palleton is a designer tool for creating color combinations that work together well. If you need some help coming up with a color scheme for your website, Palleton will give you some amazing combinations. Choose your colors on a color wheel and select from some tried color combinations such as Monochromatic, Adjacent Colors, Triad, Tetrad, and Freestyle.
Color Theory In Graphic Design：Brief Guide for Non-designers
Article
GCF Global
Make Color Work for You
Flatuicolorpicker is more than a useful tool, it is just a collection of colors that you can use in your next design project.
Browse thousands of color combinations
All in one resource for finding colors
The Missing Cheatsheet For Brilliant Color Combinations
a creative community where people from around the world create and share colors, palettes
and patterns, discuss the latest trends and explore colorful articles... All in the spirit of love.
from Smashing Magazine
Find color analogic, contrasting, and monochromatic schemes and test them with various vision abnormalities.
