The lightness or darkness of shadows are entirely regulated by the colour of the objects on which they fall.
An object painted in a light colour will be more or less light, according to the strength of its shadow, from the consequences attending opposition.
So a light figure, laid upon a light background, but differing in colour—as a warm object on a grey sky—assists, in the greatest degree, the preservation of the breadth. Opposition of colour is, perhaps, of most use under these circumstances.
Colours on the figures or parts brought into notice by opposition may be sometimes applied with sufficient depth and intensity as to advantageously take the place of shadows or darks.
Light and shade may be produced by the influence of colours alone, judiciously applied; the reds and yellows supporting the lights, while the blues, greys, and cold colours form the retiring portions, or such as would otherwise be in shadow.
Suppose a picture, composed of one part shade and the other light—the light being warm, and the shadow composed of cold colours—a red or warm-coloured figure laid against the shadowed side, and a blue one brought out from the light, would, in addition to possessing the greatest force of colour, have a spirited and imposing effect. But the contrary treatment would possess the greatest breadth and repose;—a dark figure laid on the mass of shadow (a point of which, being darker than the rest, would gather it together), and a light one on the light, having a point still higher in colour than the ground.
Rich, deep, and warm shadows are required to support strong coloured lights. So, strong colours are equally useful in focussing the shadows, or in giving them variety.
That beautiful diffusion of æriel and fluctuating pearly reflections, that play equally over the surfaces of the strongest colours, shadows, and lights, in the tenderest hues and forms, and with which all nature appears invested, should engage our deepest attention and enquiry, as their properties so softly blend and break down the harshness and influence of positive colour, and the asperity of opposing tints, by tempering them with their airy and luminous sweetness.
If the general harmony or hue of a picture is warm, the deepest shadows should be warm also; while the strongest colour, being brought into the middle space, will serve to connect both the light and the shadow. Indian red, in most instances, should be the mixing medium, using cold colours sparingly, and only where they are wanted as a foil; as the greens of trees are set off from the rich brown shadows, producing a splendid effect, and bringing the hot and cold colours into harmony.
Colours, forming the middle tint and shadows, should always be warm; though the light may be cold, the effect will be beautiful.