“Humans are trichromats, which is to say, their retinas contain three different types of receptors (called cones for their shape when viewed through a microscope) with three different pigments sensitive to three different ranges of the visible spectrum. These three pigments, conventionally labeled S(hort), M(edium), and L(ong), have their peak sensitivities at roughly 440 nm, 53o nm, and 56o nm, respectively, although there is considerable overlap.”