So, I love chemistry. My undergrad is in chemistry. One of the fundamental structures in organic chemistry is the benzene ring, i.e., C6H6. The benzene ring essentially looks like a hexagon in 2D, or a boat or chair in 3D.
Now, I also like to take concepts and play around with them. For example, ROY G BIV, or the colors in a prism/rainbow. Thinking of a benzene ring, or hexagon, I would prefer to think of those 7 colors as 6, ROY G BP. Besides, purple is easier to think of than indigo/violet.
That said, placing the 6 colors in a hexagon, I have a color-gon, like the one seen here. What's also nice about it, is you can visualize the 3 primary colors (red, yellow, blue) and the 3 secondary colors (orange, green, purple). Not only that, but you can visualize the various ways to make brown using complimentary colors like red/green, orange/blue, and yellow/purple.
That said, another way to approach this color order is with highlighting notes. For example, a normal outline mode may look like I.A.1.a.i(1) that is 6 layers deep. Well if you have a red, a yellow, and a blue highlighters you can essentially make all 6 layers of highlighting, not to mention a 7th in brown. So now, I = Red, A = Orange, 1 = Yellow, a = Green, i = Blue, and (1) = Purple.
Voila!
