So "today" I have found an image that I had colored long ago which I haven't shared yet... this is Witchy Wanda from Make it Crafty. One of my main goals while coloring this image was to give her more color than the traditional black with black Halloween colors that are associated with witches. So I started with giving her red hair then the green naturally followed as a complementary color. Then for additional color I added the white to "accessories" and finished off her wardrobe with black. This gave me several colors to work with which was certain to achieve my goal. However, with so many colors it is sometimes hard to determine where and what to color!! That's when I try to rely on a tricolor rule and hope it works out in the end.
I'm not sure if the Tricolor Rule is an official artsy term but it sure helps me a bunch especially for smaller images that I want to use many colors. Here's how I think of it... when looking at the image I try to pick out three areas of a triangle to use the same color on. These would be features that are about the same size and would have the same level of focus drawn to them. For example, in this I have the hat, bow and boots in black; another example would be the white and my triangle would be the peakos and her two gloves. Some that are not so obvious is the green being the bow on the hat, the larger skirt area and the top part of her dress; and even her skin helps create another triangle with her two shoulders and her face.
It's a mess to see the image with all those triangles but with the six triangles showing it helps to visualize the concept better. When it works out, it's a great way to disperse the colors around the image and it helps me decide what colors should go where. Hopefully this gives you some ideas for when you're stuck on your next image and can't decide how to color it. If so, I'm glad it worked out and that I could share this little tip. :D Good luck!