"...organizing his books by color allows him to discover new and unexpected relationships between books he knows well already. When two unrelated books are forced to occupy the same shelf simply because of their spine color, the shelver is asked to think about whether they have ideas to share between them. Perhaps, the designers of these chromatically-related books saw something in the books' content that even their authors did not. Maybe their ideals share a common hue?"
– Rob Giampietro, On Arranging Books by Color