There is more to colour than meets the eye and an account of some of the purported psychophysiological effects is given. The question whether Red is a more activating colour than Blue is discussed by reference to two opposing schools of tought, one based on colour light and measured by physiological changes in the central and autonomic nervous system and the other based on colour pigment applied in interior and exterior spaces while varying the dimensions of hue, chromatic strength and lightness. An experiment is discussed where subjects experience realistic full scale Red and Blue spaces and where both physiological and affective measures are taken.