The main goal was to further understand the limited palette we're using in oil, which is titanium white, yellow ochre, cadmium red light, and ivory black. You can create pretty much every color out of those four, just the cools are relative and muted, so a lot of the color relies on the color that's around it.
This was a great exercise not only to understand the palette, but also understand how to mix color, as well as see subtle color variations and paint them. Learning to mix the right hue, right value, and right chroma and then putting down just one correct brush stroke where it needs to be is hugely important, and it's one of the secrets of making effortless looking work. Needless to say, I'll need a lot more practice!