Oil on paper, 9" x 12"
I could have done with using a smidge more of the red in the second column as it looks very similar to the fourth column. In the third column, I discovered Turmeline Green (I was given this in a pack of three free samples a year or so ago; it's by Schminke Mussini). In the fourth column, I got lovely soft greys, a bit like Payne's Grey.
The mixes on the top row are pure Ultramarine Blue, UB with a touch of Permanent Red Medium, UB with a touch of Permanent Yellow Light and UB with a touch of both PRM and PYL; in all of the mixes that particular 'primary' is dominant. Going down each column, I've used increasing amounts of white to create tints. I used the same tiny palette knife.