Some years ago I started working with a double primary palette in watercolor and in oil. For the benefit of the new class members and others who struggle with color, I will explain the colors and the reason behind their choices. Sometimes I am amazed that people have taken classes where the instructor did not talk about laying out a palette and color mixing. Everyone has their own system but I find if I lay out my colors the same way each time, I can find them easier and mix faster.
The pure white goes on the top center of my palette. I squeeze out more of it than other colors. On the opposite end, goes my black, if I am using it, and a row of earth colors: raw sienna, burnt sienna, burnt umber and raw umber. I always look at my subject: what do I need? The earth colors are useful for mixing. I can make greys and nice greens by adding them. Next I do a row of the warm colors down the side beginning with the lightest: Lemon yellow, cadium yellow medium, yellow ochre, cadium red light, alizarin crimson. Permanent rose is one I may add if I am working with violets or lots of shadows. The cool colors are together on the last side starting with the lightest blue: cerulean blue, cobalt blue, ultramarine blue, then the greens (again, what am I painting that I need greens I can't mix?): permanent green light, sap green, and viridian or hooker's green. For a landscape palette, that is all I will need to mix lots of greens, shadows, and sky.
What makes it a double primary palette? There are two values of each primary here: a lighter or cooler value such as lemon yellow and a deeper or warmer value: cadium yellow medium. Same with the reds: lighter cadium red light and deeper alizarin crimson. Blues: cerulean blue and ultramarine blue. You could use just the lighter colors and mix the darker or you could use just the darker and mix them lighter. It is just a matter of convenience that we have so many colors to choose.
I am working in my studio today to finish a few of the Tuscany paintings for the October show at the Hollis Gallery. I will shoot my palette (before it gets used) and post. After my head clears of hilltops, vineyards, and cypress trees, I will explain the colors and how to mix them without creating "mud".