The importance we attach to our perception of light and colour and its emotional effects is discussed with reference to experimental work. The question of whether red is a more activating colour than blue is discussed by reference to two opposing schools of thought. One is based on colour light and measured by physiological changes in the central and autonomic nervous system and the other is based on colour pigment applied in interior and exterior spaces. The question whether colour affects the subjective estimation of time and warmth is also discussed with reference to experimental work. The ongoing debate of colour aesthetics and, in particular colour preferences is discussed on a longitudinal basis for the past 40 years of teaching the subject in the Oxford School of Architecture.