Is Color Perception a Sixth Sense?: A Victorian Psychologist Tells All

According to the psychologist Grant Allen in his 1879 book, The Colour-Sense: Its Origin and Development, "There is no element of our sensuous nature which yields us greater or more varied pleasure than the perception of colour" (1). As people interested in design, I would wager that many of us are tempted to agree with him, but have you ever thought about why, precisely, color gives us so much joy?