Yellow, Red and Blue are called the primary colors, the presence of which, either pure or in combination, is found to be necessary to satisfy the eye. They have each a different relation to light, and must therefore be used in proportions which fulfill these conditions. Any two of these primaries being mixed, a secondary color is produced, thus
Blue and Yellow form Green,
Blue and Red form Purple,
Yellow and Red form Orange.
In like manner, by the mixture of any two of the secondaries, tertiary colors are formed, thus: Orange and Green produce Citrine, or the set of tints of a greenish-yellow character approximating to citron; Orange and Purple form Russet, or warm brown; whilst Purple and Green produce Olive, or dull brownish green.
By the varied and due admixture of these colors an infinite number of hues, shades and tints are produced, whilst by an indefinite and disproportionate mixture of the three colors, or of the whole together, will be produced the hues usually called dirty, or the anomalous color, brown.
There are five classes of colors: The neutral, the primary, the secondary, the tertiary and the semi-neutral.
Neutral colors are three only, White, Black and Gray. According to the laws of optics, the two first comprise all others synthetically and afford them all by analysis. These are sometimes called extreme colors, gray being their intermediate.
Thus, if Black and White are mixed. Gray is formed, or if a transparent Black is washed over a white surface, a corresponding effect is produced.
Primary colors are three only. Yellow, Red and Blue. They are such as yield others by being compounded, but are not themselves capable of being produced by composition of other colors. By way of distinction they are occasionally designated entire colors. Secondary colors are
