The problem arises, when the scheme involves the use of more than one colour, and the successful effect depends on judicious association and balance. The simple rule is never to display two only of the primary colours in juxtaposition, the presence of the third being essential to harmonious and satisfactory effect.
This, as a principle, forms the basis of much of the Moresque decoration, in which the details were picked out in blue and red of positive hues, and separated or outlined with gold.
More consideration is required when positive or pure colour is not in request, and the proportions of juxtaposed tints have to be relative. As any tint departs from the full strength of its particular category, so those associated should be proportionately remote.
Respective quantities may vary and one colour occupy relatively a small part of the surface, when to preserve the balance it may be stronger in hue than others occupying adjacent and larger areas. For such contingencies it is impossible to give exact formulæ, as the pigments employed are not always constant. In the case of manufacturers of mixed paints, it is customary to issue samples of colours for the year or season, and they cannot guarantee repeating exactly any colour or tint in subsequent mixing. The same applies where coloured papers and textiles are concerned; therefore judgment based on principle and experience can be the only guide.
The Primary colours are Red, Yellow and Blue; admixture of any two of these result in the Secondary colours which form the complementaries of the Primaries not involved. Thus blue and yellow combined result in green, which is the complementary of red, the complementary of yellow being purple, and that of blue, orange.
Intensity of hue of any colour employed may vary considerably, and this variation should be proportional in other tints associated. Part of the charm of colour often depends on its complexity, in natural aspects due to atmosphere and varied phases of light. Pure colours should at times be avoided, that is, in the sense in which they are obtainable as pigments.
Students should have attained some considerable facility in drawing before taking the study of design seriously, though probably part of the early training has dealt with extremely elementary forms leading in that direction. Undoubtedly, too, many enter on this phase of study without adequate preparation, having little appreciation of the underlying geometric construction, not only in design but in all form.