“[T]he treatise On Plants attributed to Aristotle observe that ‘Greenness must the the most common characteristic of plant life’ and finds the reason in ‘concoction,’ the slight heat generated by the plants taking of nourishment out of earth and water.’ Green is ‘the intermediate color between that of earth and water,’ as can be witnessed in tree leaves, which grow out of the plant’s white pith and break through its blackish bark.”

—Bruce R. Smith, The Key of Green, 2009.