Chap. CCXLI.—Of the Colour of Shadows.
The colour of the shadows of an object can never be pure if the body which is opposed to these shadows be not of the same colour as that on which they are produced. For instance, if in a room, the walls of which are green, I place a figure clothed in blue, and receiving the light from another blue object, the light part of that figure will be of a beautiful blue, but the shadows of it will become dingy, and not like a true shade of that beautiful blue, because it will be corrupted by the reflexions from the green wall; and it would be still worse if the walls were of a darkish brown.