I thought this one went pretty well for 90 minutes. I used a limited palette of only two colors: Yellow Ochre and Cadmium Red (and black and white). So two or four, depending on how you count them. The Anders Zorn palette.
The fun and surprising thing about this limited palette is that a cool gray becomes bluish in context of the other colors, and mixing some ochre into that gray turns it into a nice olive green. So you have a wider range than you might think, but you have to be creative.
