Extending either the light or shadow by means of colour, is perhaps one of the best ways of combining both.
Breadth of light and shade may involve many colours in its arrangement, so they are divided into imposing masses; variety of colour is often necessary to explain the localities of a work; and, that they may not appear confused, light colours should be sociable with light colours; and dark ones with others of equal density: their repetitions invading each other throughout the chain.
Great intimacy of union, in the colour of the lights, will likewise produce breadth; so as to make a large and connected mass appear, at a little distance, as one graduated light.
Colours may stand either for colours or shadows; so that they be of sufficient density, and sufficiently opposed to light ones.
But, if you do not depend on the colour of the picture for effect of light and shade, much less intensity of colours will be sufficient.
The strongest colours are sometimes most successfully employed in uniting the light with the shade.
In the conduct of light, I conceive the objects which receive its influence, should, of all things, as much as possible, partake of the colour of that light, as seeming more like an extension of it, and looking more natural:—thus, in a church, all the parts receiving the light from a painted glass window, would partake of its varieties of colour. The rising and setting of the sun turns all to gold, by the same alchymy, while it acts as an uniting link in carrying the colour through the picture: these, in their turn, throw their radiating reflects in a thousand other directions, keeping up and sustaining the communicative principle of the whole—imparted by the primitive cause and its agency.
The colouring of a picture should always be in harmony with its light and shade.
The lights will require to be overcharged with colour, if the shadows are too heavy and loaded; on their transparency depends the beauty of both.
The shadows must be darker than the shadowed sides of the objects which project them; for the reason explained in the article on Light and Shade.