I decided to try Prussian blue because John Carlson used it.   This color was one of the first pigments developed during advances in organic chemistry early in the nineteenth century.  It's a very powerful dark blue.   It's like a cool black, almost like ivory black.

In this painting, I added Prussian blue to my usual palette of Cad Red, Cad Yellow, and Ultramarine.   Notice how deep shadows in the trees and building appear.

I began oil painting with a palette limited to Cadmium Red, Cadmium Yellow, and French Ultramarine Blue, a combination often called a "chromatic palette."  Although there are hues that can't be created with this palette (some bright greens, for example) it's a great palette for learning to mix colors.  It also makes harmonious paintings.

This lighthouse image is an example.  It's just Cad Red, Cad Yellow, and French Ultramarine.   It suggests a glow from the late-afternoon sun.