Great darkness is only obtained by the opposition of bright light, and bright light by contrasting it with density of shadow.
Colours should recede in proportion to the size of objects, as they retire from the eye.
Too frequent a repetition of the same colour will produce monotony; so will too much contrast.
Contrasts in colouring must be used with great caution, or the absence of all keeping will be the result. At the same time, the beauty of a colour is only fully developed by being placed by the side of its opposite, or the one from which it is farthest removed.
If the blacks in a picture are kept firm and decided, they clear up the general effect, and give lightness and buoyancy to the whole work.
A colour is often left single, and standing by itself, in some principal object; in which case, it is so contrived, by its density, or some other quality, to bring together and harmonize all the rest.
If colours are not placed in harmony with each other, they must be in contact with such as give them value; as red against a cold, or green against a warm colour. In short, the grand principle, in all its constituent parts, simply amounts to this.
The strongest darks, brought in contact with the strongest lights, increase their brilliance, by giving to the lights the utmost force and clearness they can receive.
Richness of colouring can only be adopted when the general tone of the picture is sufficiently dark to support it.
All colours retire in proportion to their negative or neutral character; and as they develope themselves, gradually approaching to their brightest point, so they reach the prominent parts of the foreground.