A colleague of mine and awesome webmaster, Aaron Congleton, just sent me to a great article on designing with color, Contrast is King, on A List Apart. Definitely a nice read with some great resources and information to help you design in color and consider accessibility and viewing aesthetics and balance.
http://www.alistapart.com/articles/contrast-is-king/
A great concept that is mentioned is the practice of viewing your design in black and white to see where color may fail and how the design appears including contrast in a low fidelity scenario. I used this approach recently creating some test for form validation and the issues that can arise when using color only for indication. Luke W. can tell you all about that.
There is also a tool that was mentioned in the post for http://colorschemedesigner.com/
This is an awesome resource that provides designers many tools and options to create their color palette similar to Kuler, but also accessibility features like the ability to view your palette via various color blind type perspectives.
Oh yeah – it is built in javascript!
