Color is the painter's means of expression - but color as surface. Thus he differs from the draftsman, who works with lines, the color of which is immaterial.
The classical drawing is in black on a white ground, with possibly some intermediate grays. If sepia, red, or other colored chalks are used, the whole drawing is done in only one color and remains an abstraction of the natural model from the point of view of color, in the same way as the outline is an abstraction of the surface and of the volume. Black, gray, and white are abstractions of the color as is also the translation of the multi-colored natural impressions into a single color tone.
Black and white hardly ever occur at their purest in nature. Neither phenomenon can be designated as "color." Then what is color? For the painter it is first a powder which he spreads on his painting surface with something to make it stick. This says nothing about the physicalor chemical properties of the coloring substance. If we look at color powders in the dark it is impossible to tell which is blue and which yellow. Colors can be recognized only in the light. Illumination alone creates them.
You were no doubt taught in school that white, colorless light can be divided up into a colored spectrum through a prism. Light is the radiation of a source of energy. The visible wave lengths of this radiation lie between 397 and 687 millionths of a millimeter. Each one of these wave lengths
has a distinct color. These phenomena begin with violet and spread continuously over blue, green, yellow, and orange to red. Shorter light waves (ultra violet) and longer ones (infra red) cannot be directly perceived by the human eye.
If we say of a material that it is blue, it means that this material reflects only blue light waves; all the rest it absorbs and transforms into heat. This can be easily proven: if we touch a white object in the sunshine, it is scarcely different in. warmth from the surrounding air. White reflects all light waves.
A black object, on the other hand, can become so hot in the sun that it is too hot to touch, for all the light waves that reach it are absorbed, turned into heat, and then slowly given off again. If we cover an object of another color with a layer of blue, this layer gives the impression that the whole object is blue. This property characterizes the substances which are called simply "color."
The color circle gives an optical elucidation of the properties of color. It is a scheme which includes first the three primary colors: blue, yellow, and red. These are called primary because they cannot be made by mixing other colors, and both by optical and material mixing they can give all other colors. If equal quantities of any two primary colors are mixed together they produce a new color; so there are three new colors: green, orange, and violet.
The circle is now divided into six colors. It becomes twelve-part if each pair of neighboring colors is again mixed. Further intermediate grades can be made by mixing yet again each neighboring pair, until by the time the circle is divided into 48 we have an almost continuous transition of color - a phenomenon which can be seen in perfect form in the spectrum or rainbow.
All these colors are called "pure," as each sector consists of only one or two primary colors, however fine the division of the circle, as against the impure, dull colors in which there is some of each of the three primary colors.
Just as light can be split up into its wave lengths and colors, it can be combined again. If three panes of glass in each of the three primary colors are superimposed, the light coming through them is colorless. Even the mixed color of two of these panes is lighter than the color of either of the two panes by itself, since two thirds of the visible scope of the waves is combined light. This combination of colors is called an "additive" mixture, in contrast to the subtractive, in which light is taken away.