The purity or intensity of a color depends upon its relative freedom from white light. Purity therefore expresses the amount or degree of the hue present, as distinguished from the total amount of light, both white and colored, present. While no pigments are wholly free from white light, the normal hues are called pure. They lose purity as they are progressively neutralized by union with their complementaries, or degraded by the admixture of black, white or neutral gray. Thus garnet, la France, and jasper red are impure variants of scarlet-red, formed respectively by the addition of black, white and neutral gray to the normal.

Luminosity or value is that characteristic of a color which depends upon the total amount of light, both colored and white, reflected to the eye. Value, in painting and the allied arts, is defined by the Century dictionary as the relation of one object, part or atmospheric plane of a picture to the others with reference to light and shade, the idea of hue being abstracted. Thus normal yellow, though it is identical with normal red in purity, exceeds it in luminosity. White exceeds all the hues in luminosity, while the tints of any hue are more luminous than its shades, in direct proportion to the white in the mixture, and without any reference to the relative purity or neutrality of the hue. The value of a given color may be determined by comparing it with a scale of neutral grays, ranging from black with a value of o to white with a value of 100; or, roughly, with the gamut black, dark-gray, gray, light-gray and white.

Variations in the luminosity or brightness of a color are called tones of that color. The summer sky, surveyed from horizon to zenith, reveals numberless tones of blue, as a distant forest or a field of young grain reveal numberless tones of green or yellow-green. This usage of the word tone must be carefully noted, for it will be constantly and consistently employed. It differs from the usage of painters, who ordinarily employ the word tone to express similarity of tone, or the prevalence of .like tones.

It is in fact imperative that the reader who desires to understand the discussion of color included in this study of interior decoration accept the few definitions of color terms precisely as they are stated. Definitions are absolutely necessary to clear concepts, and inasmuch as writers on color habitually use its terms with varying connotations, the words employed in this volume with one significance may be encountered elsewhere with another. The study of color is perplexing at best. It becomes unintelligible when there is any doubt as to the meaning of the terms employed.

The unscientific and confusing system of color nomenclature is, unhappily, a source of perplexities which no care can unravel. Color has always been more a matter of fancy and of fashion than of exact knowledge, and as a result the hundreds of color names used in the arts have been drawn indiscriminately from any source that proved suggestive - from the earth and the heavens above the earth and the waters beneath it - and applied in ways nearly always inexact and frequently misleading. Of all the hues the blue-reds have the most accurately-descriptive terms, perhaps because the violets and purples have always been of more interest to poets than to common men; yet even here there is no pretense of a scientific or even of an accurate nomenclature. For example, to take a few only of these color names, the term purple comes from a shell; violet, lilac, lavender, mauve, iris, amaranth, petunia and hyacinth from flowers; mulberry, raspberry, plum and prune from fruits; and amethyst - the word itself means a remedy for drunkenness - from a stone. Puce is French for flea; gridelin is contracted from gris de lin; Bishop's purple and London smoke are loosely descriptive, and elephant's breath is a pure creation of the fancy of an earlier day.

With the best intentions in the world it is quite impossible to use such terms exactly, or even intelligibly, so that among professional workers in color - to say nothing of laymen - a given color name will rarely convey precisely the same idea to two different individuals. The inevitable confusion is heightened by manufacturers, who not only constantly launch new color names, but also employ widely varying colors under the old names. Many more or less complete and elaborate systems of color notation have been devised, notably those of Chevreul, Maxwell, Oberthur et Dau-thenay, and Ridgeway; but these systems have never been widely adopted. Considerable progress toward standardization has been made in the last decade; but at the present time the great number of color sensations can be described with approximate accuracy only in terms of their relations to the primary and binary hues, and to black, white and gray. This system is clumsy and tedious, but it is the best available to one who desires to be widely understood.

The effects of color upon our emotional states are indubitable. As to the degree in which these effects are due on the one hand to association of ideas and on the other to differences in the rapidity of light-ray vibrations it is impossible in the light of our present knowledge to speak definitely. Red is the color of fire and of blood, as violet is the color of shadows, and it is inconceivable that the mind could remain unaffected by these associations in the presence of either color. On the other hand, red lies at one end of the spectrum and violet at the other, and it is equally inconceivable that the brain, as a physical organism, could remain unaffected by the enormously different rates of vibration. In any case the matter is of scientific interest only. It is enough for the decorator to know that the various hues possess distinctive emotional qualities; that the colors vary in emotional value not only with hue, but also with purity and luminosity; and that through proper selection of the hues, proper emphasis upon purity or neutrality and upon high or low tones, he can - with the convergent use of line and form - express in his rooms any motive that appeals to his artistic judgment as fitting.