A Treatise on Painting/Chapter 287
Chap. CCLXXXVII.—Of the Variety observable in Colours, according to their Distance, or Proximity.
The local colour of such objects as are darker than the air, will appear less dark as they are more remote; and, on the contrary, objects lighter than the air will lose their brightness in proportion to their distance from the eye. In general, all objects that are darker or lighter than the air, are discoloured by distance, which changes their quality, so that the lighter appears darker, and the darker lighter.