The perception of colour, similar to the perception of brightness, is dependent on neighbouring colours and the quality of the lighting. The necessity for us to be able to interpret colours is based on the fact that colour appearances around us are constantly
changing. A colour is therefore perceived as being constant both when viewed in the bluish light of an overcast sky or in warmer direct sunlight - colour photographs taken under the same conditions, however, show the distinct colour shifts that we must expect under the particular type of light.