technique

Alyssa brought up mixing a little bit of a core color into every color of a painting to keep things consistent and harmonized. Great advice!
Some of you may know Matt Larsen, anyway, a few years back he went to one of Jeremy Lipking's workshops, and that was one of the techniques he utilized. Check out some of his amazing work to see this in action.
-his blog
-his gallery

If you're painting in oil, some people achieve the same final effect by running a light glaze of the core color over everything as a final or near-final touch.

*in PS it's just a matter of adding a 'color' type layer of the core color on top of everything and reducing it to a low opacity