In physics, quarks come in one of three color states, usually chosen to be called, "red", "green", and "blue". However, because these are just labels, there are other naming conventions that are used. Murray Gell-Mann used "red", "white", and "blue" because those are the colors of the French flag. Roger Penrose, in his book The Road to Reality, denounces this and states that he uses "red", "yellow", and "blue", as they are the primary colors of paint, rather than the more common "red", "green", and "blue", being the primary colors of light. In almost every source I can find, these seem to be the conventions that people typically use, with rgb being by far the most common.
However, in Group Theory in a Nutshell for Physicists, Tony Zee uses "red", "green", and "yellow". This is a convention that I have not seen mentioned anywhere else, but a professor of mine claims to have learned the same notation that Zee uses.
I was hoping to learn about the origin of this discrepancy. Obviously, these are just labels, and one can call them whatever they so please. That being said, I'm still interested in what the origin of the "rgy" naming scheme is. Is it a region difference? Is it a generational difference? There seems to be almost no mention of the "rgy" coloring scheme outside of this book, which doesn't even make mention of the fact that there are other conventions, much less that they are more common.