Fellow illustrator and blogger, James Gurney, has routinely spoken at great length about the benefits of 'Gamut Masking'. Now, artist Richard Robinson has created a very simple, easy to use, and totally free Gamut Masking Tool. With a variety of pre-existing masks to choose from, and the ability to create your own custom masks as well, you can see what color scheme will work best for you very quickly! Try it out HERE.
Be sure to check out the rest of Richard's site, Painting Lessons: Beginner to Advanced, it is chock full of valuable information.
For more information on Gamut Masking, read James Gurney's blog posts on the subject here:
Intro, Part 1, Part 2, Part 3