Today’s New York Times has an article by Natalie Angier called How do we see red? Count the Ways. Angier discusses the psychological and philosophical aspects of the colour red, the physiological basis of perceiving the colour, and its significance in the animal kingdom;
As full-spectrum sunlight falls on, say, a ripe apple, the physical and chemical properties of the fruit’s skin allow it to absorb much of the light, save for relatively long, reddish lightwaves, which bounce off the surface and into our greedy eyes. On hitting the retina, those red wavelengths stimulate with greatest fervor the cone cells set to receive them, a sensation that the brain interprets as “healthy, low-hanging snack item ahead“. In fact, human eyes, like those of other great apes, seem to be all-around fabulous fruit-finding devices, for they are more richly endowed with the two cone types set to red and yellow wavelengths than with those sensitive to short, blue-tinged light. That cone apportionment allows us to discriminate among subtle differences in fruit ruddiness and hence readiness, and may also explain why I have at least 40 lipsticks that I never wear compared with only three blue eye shadows.