You might think that a book about watercolors would be quite simple in its design and if you think that, you must never have heard of the book Traité des Couleurs servant à la Peinture à l’eau, which was written in 1672. The writer/artist who created it is not known, only known as “A. Boogert.” The artist intended the book to be a teaching aid, yet it failed in this because there was only a single copy of it. It is breathtaking in its scope, and at over eight hundred completely handwritten pages, it describes not only the use of color in painting but the way to create different colors and hues by adding different amounts of water in different colors, as well as the different uses of tones and styles.
The book is incomparable, and to find a book that was similar in scope and depth, you would have to wait until 1963 when the current standard-the Pantone Color Guide-came out.
The original book is currently kept at the Bibliothèque Méjanes in France, you can read the whole text online as well as numerous descriptions of the book and its creation. (h/t: Erik Kwakkel)