The Color Currency of Nature

"Red toadstools, red ladybirds, red poppies, are dangerous to eat, but red tomatoes, red strawberries, red apples, are good. The open mouth of an aggressive monkey is threatening, but the red bottom of a sexually receptive female is appealing. The flushed cheeks of a man or a woman may indicate anger, but they may equally indicate pleasure. Thus the colour red, of itself, can do no more than alert the viewer, preparing him to receive a potentially important message; the content of the message can be interpreted only when the context of the redness is defined."

Nicholas Humphrey, 1976