This is a great time of year to compare "ultra realistic" polymer clay miniatures to the slightly exaggerated "cartoon style" often shown for miniature tree ornaments. There's nothing wrong with either style, but the ornament style tends to use readily available colors of clay, while artisan realism requires a good understanding of basic clay color blends. If you have some holiday time coming up, and want to improve your color blending skills, buy the basic colors , red, yellow, blue, black, white and translucent or for the CMYK blending system, turquoise (cyan), magenta, yellow, black, white and translucent and start experimenting. Keep some "recipe" cards and measure clay color amounts so you'll be able to recreate your favorites over and over like artisans do.
If you really want to get into color theory, how to make designs in polymer clay really stand out, look up a copy of Polymer Clay Color Inspirations It's currently high on my seasonal wish list!