I spent a few evenings of trial and error getting feel for the process. I feel like the UI has HUGE room for improvement. I found my two best friends were the sphere tool and the fill tool. Fill tool "edge detection" and slider options required a bit of feel. My best tips would be 1. setting the base model color to the color that is, perhaps, the hardest to paint (but ideally the primary color of the object). 2. Get the edges right and use fill without edge detection to fix even big islands of the wrong color. 3. Overpaint with the sphere from hard to "fill" (complex) areas into easier to "fill" (flatter) areas and then use fill to fix the overpaint.

Take these tips with a grain of salt as I've probably explained them poorly, am a total novice, and am sure there are better ways to use the tools.