Here is a representative pallet readied for a recent figure session. It contains two different sets of primary pigments.
|Two blues, two reds, two yellows and white|
|Nude Study, oil on canvas, 10" X 8", 2015|
I know artists who routinely use over thirty colors on any given painting. The problem for me is that with so many potential combinations it is impossible to understand with any clarity how one color reacts with another. I therefore find myself trying to limit the number of variables. Red, blue and yellow is about as simple as you can get.
Given that my painting tastes and knowledge are always in flux I don't expect my pallet to ever be "settled".