I've been dropping tubed burnt umber off of my palette lately and mixing it from the red, yellow, and blue. I also mix up a chromatic black that way. I then follow Mark's color matching method to mix my colors. and am quite satisfied with my results.
So right now, I'm using pyrrole red, ultramarine blue, cad yellow and titanium white. If I want to use something like the Zorn palette, I just mix my ivory black, yellow ochre, and vermillion.
If anyone else working with a minimal palette like this?