Colour is a complex sensation, but we should remember that an object has no single characteristic colour because its appearance is affected by a number of factors. If we ask what the colour of the girls kimonos are from the image below (from a series of ca.1880s-90s full-plate images printed by sunlight on simple “salted paper”, and hand-tinted with transparent water colours), our first reaction may be to say that they are purple. By this means we identify the hue of the object. However, this description is clearly inadequate. To be more specific, we could say that one kimono is light purple and the other is dark purple. This describes the brightness of the colour. Colour could also be described as bright, dull or vivid, a characteristic known as saturation. Therefore the perception of colour is comprised of three characteristics, any one of which can be varied independently. But we are really describing sensations, not the object, nor the physical stimuli reaching the eye.