Any thing white seen in a dense air full of vapours, will appear larger than it is in reality.
The air, between the eye and the object seen, will change the colour of that object into its own; so will the azure of the air change the distant mountains into blue masses. Through a red glass every thing appears red; the light round the stars is dimmed by the darkness of the air, which fills the space between the eye and the planets.
The true colour of any object whatever will be seen in those parts which are not occupied by any kind of shade, and have not any gloss (if it be a polished surface).
I say, that white terminating abruptly upon a dark ground, will cause that part where it terminates to appear darker, and the white whiter.
COLOURS IN REGARD TO LIGHT AND SHADOW.
Chap. CCXLIX.—Of the Light proper for painting Flesh Colour from Nature.
Your window must be open to the sky, and the walls painted of a reddish colour. The summertime is the best, when the clouds conceal the sun, or else your walls on the south side of the room must be so high, as that the sun-beams cannot strike on the opposite side, in order that the reflexion of those beams may not destroy the shadows.