In them he is exploring questions that are not raised often enough, including questioning the concept of exactly what is a primary color, and how might primary colors be interpreted differently; not just in different color spaces, additive and subtractive, but even within the familiar paradigms of modern color theory and practice.
The colors that are considered primaries, as he points out, are not set in stone.
The series, of which there are three installments to date, is likely part of the material Gurney is producing for his upcoming book, Color & Light.
I don’t know how many posts there will be in this series, but you may find that it encourages you to think about color and color mixing a little differently.
(You may find it useful to supplement your reading with my post on the History of the Color Wheel.)