seven possible colors — Ludlow is reaching here when he declares that there are “seven possible colors” that are a “primeval and necessary accompaniment of the manner of transmission.” Color is not so much a property of light but the result of how the human eye and nervous system categorizes light radiation of various combinations of frequencies. Most people’s eyes have three types of frequency-sensitive cones (some have fewer, some women have four); most mammals have two; birds and reptiles, four. It is the properties of these cones and their number, and not some universal principle, that determines how people divide up the spectrum, and what harmonies we find there.