“… This video uses “harmonic coloring,” in which each pitch class (C, C-sharp, D, etc.) is a different color, with the colors being assigned according to the circle of fifths…” In short, “the circle of fifths is a way to arrange keys to show how closely they are related to each other”. More info from the above bideo: here. Also see the Music Animation Machine and Smalins Youtube Channel.
Though not specifically related to guitar this is an interesting article on music analysis, as in what makes a song tick? “…On first listen, some things grab you for their off-kilter novelty. Like the story of a company that has hired a bunch of “musicologists,” who sit at computers and listen to songs, one at a time, rating them element by element, separating out what sometimes comes to hundreds of data points for a three-minute tune. The company, an Internet radio service called Pandora, is convinced that by pouring this information through a computer into an algorithm, it can guide you, the listener, to music that you like. The premise is that your favorite songs can be stripped to parts and reverse-engineered…” The Song Decoders (Sunday N.Y. Times)
I’ve meant to read this book for a couple of years now. I came across it again on Amazon.; It looks pretty good, though even the pb edition is pretty expensive. Classical Guitarists- Conversations. By the way you can read some excerpts from this book at Google Books.