From Kevin MacPherson’s Landscape Painting Inside & Out:
AT THE START OF A PAINTING, CHOOSE ONE PRIMARY AND MIX IT WITH THE OTHER TWO PRIMARIES. Draw from these puddles for all subsequent mixtures, so that every mixture in the painting has something in common. The other two primaries will obviously be less pure. For example, if we added a bit of yellow to the red and blue we would have yellow, red-orange and blue-green as our palette, resulting in a warm tone to the final painting.
Chapter 3 – “The Theory of Relativity”