I've been having fun playing around with limited palette paintings. I enjoy how well-unified it can make a piece, while still maintaining a plausible feel to the colors. I was inspired to try this after reading an old post in James Gurney's blog.
The first is just a google image search squirrel study. In the second, I wanted to see if I could get the blue in Superman's costume to look blue without using blue (in fact, the "blue" is actually a grey in the red part of the spectrum). The third is just a creature sketch from my imagination. The fourth is a sketch from a photo of me in my halloween costume (i was dressed in a chiton as an ancient greek).
Here's a caricature I did of Jason Seiler for a contest, also using a limited palette:
I'm fairly pleased with how it turned out. I invented the lighting situation compared to the reference to give it a more interesting mood and atmosphere.