A Set Of Web-Based Tools For Working With Colors – Color Explorer
Color Explorer is a free-to-use website which offers various tools to work with colors more efficiently.
You can upload an image to get the colors used in it automatically, browse color libraries (W3 named colors, web-safe colors, Focoltone, etc.), convert them between formats or make contrast analysis.
Optionally, and for free, you can sign-up as a registered member, create color palettes and save them for future use.
And, yes, there is definitely a cool color picker (which can also offer variations).