Chroma.js
Chroma.js is a tiny JavaScript library (14kB) for all kinds of color conversions and color scales.

Usage
Initiate and manipulate colors:
chroma('#D4F880').darken().hex();
Working with color scales is easy, too:
scale = chroma.scale(['white', 'red']);
scale(0.5).hex();
Lab/Lch interpolation looks better than RGB
chroma.scale(['white', 'red']).mode('lab');
Custom domains! Quantiles! Color Brewer!!
chroma.scale('RdYlBu').domain(myValues, 7, 'quantiles');
And why not use logarithmic color scales once in your life?
chroma.scale(['lightyellow', 'navy']).domain([1, 100000], 7, 'log');
Like it?
Why not dive into the interactive documentation (there's a static version, too). You can download chroma.min.js or use the hosted version on cdnjs.com.
You can use it in node.js, too!
npm install chroma-js
Or you can use it in SASS using chromatic-sass!
Build instructions
To compile the coffee-script source files you have to run (might have to ``npm install` first)
grunt
To run the tests simply run
npm test
And to update the documentation (thanks!), just do
npm install --global markdown-to-html http-server
cd docs/
make && make preview
Similar Libraries / Prior Art
Author
Chroma.js is written by Gregor Aisch.
License
Released under BSD license.
Versions prior to 0.4 were released under GPL.
Further reading