Contrasting colours are here understood to mean those which, when placed side by side, intensify each other but do not change. Colours which are not contrasts do tend to change their appearance when placed side by side. Thus red placed side by side with yellow appears more rosy, while the yellow looks more inclined towards green than when seen alone. But if red be placed by purple, the former will appear more orange and the latter more violet.
It is to Rood again that we owe the table of true contrasts. By measuring the proportion of each colour in the spectrum, and by dividing a circle in the same proportion, Rood produced his colour circle. He claimed that by taking the tints in pairs, as they stood opposite one another round the circle, a series of true contrasts would be produced. Careful trial will show how right he was. When his table is compared with the old three-colour table, with its complementaries, one might fancy at first glance that the difference was not so very great, but the difference is just enough to ruin a great many colour-schemes. Orange-yellow is not so far removed from orange, but it does just supply the perfect contrast to a central blue which full orange just misses. The most notable difference is probably that which occurs in the case of red and green-blue instead of red and green. A full red and a full green (neither of them inclining to either side) are distinctly not satisfactory as a contrast, but a full red against green-blue (a colour just on the borderland between green and blue, though inclining to the latter) glows with a wonderful intensity and a marvellous beauty.
Although but a few of the most familiar and pronounced tints are marked and named in the colour-circle, it is easy to determine the place of intermediate tints.
In working out a circle it is necessary that the tints used should be, as far as possible, of the same relative brilliance. If a colour be mixed with white its brilliance will of course be affected, but a white ground can safely be used.
It is most important that the contrasting colours should be used in their natural order or the effect will be discordant. Full contrasts are not very common in Nature, certainly not in any quantity, whereas harmonies are to be found in every direction. The student will probably find by experience that he also will be wise to use contrasts sparingly.
Now and again a sunset will provide very wonderful and brilliant examples of full contrast.
The famous series seen in England some months after the eruption of Krakatoa showed such pairs as vivid red upon green-blue, orange-yellow upon blue, orange on cyan-blue, and purple on green. The last named, which is a singularly beautiful combination, may sometimes be seen when a part of the sky at sunset or sunrise, immediately before a heavy gale, becomes a clear, brilliant green. The effect of bright purple clouds driving across this is very magnificent.
Reduced contrasts, i.e., where one or both of the contrasting colours are somewhat broken, though still recognizable, are often to be found ; indeed, the more broken they are the more often they are to be seen. As examples, one may cite grass or weeds on purple earth. Both grass and earth are so much broken in colour that the contrast is not wearisome. In the case of orange-yellow clouds on a blue sky, the blue is often very much broken with warm light, so that the force of the contrast is greatly reduced.
Since a contrast must, from its very nature, give a certain shock to the eye, it ought to be looked upon by the colourist as a very valuable asset, and its position should be thought out most carefully, whether for a picture or for a design.
By way of exercise in the use of contrasts the student should set out a series of contrasting pairs of colours all round the circle, and he should test the relative effects of (i) equal quantities of each colour, and (2) a large quantity of one colour and a very small amount of the other. In practice the second colour may be laid as a band a little way inside the edge of a large patch of the first colour.
A further exercise will be to choose a colour and its two next neighbours in the circle, as well as its contrasting colour, and then to work out a simple arrangement. A whole series may well be worked on the same lines.
* Cobalt and Prussian blue are the nearest equivalents in our colour-boxes, but Prussian blue tends to be dull. The transition from green to blue is more successful if made with Cobalt and Viridian.