: In 1613 d’Aguilon published a book on optics containing a novel color mixture diagram in arc form. Diagrams of similar form are found in many medieval manuscripts where they have been used to help clarify complex relationships between things. The source of this kind of graphical representation appears to be the late classical Roman author Boethius who may have used it in his work on Greek musical theory. Most of the approximately 140 extant manuscripts of this work contain such diagrams. This form of diagram was used to express color relationships for some 90 years after d’Aguilon. Key words: Color order systems, color scaling, history
Rolf G. Kuehni