In one sense it is the same as _atmosphere_ in that the tonality of the picture is the atmosphere which pervades it. It may perhaps be best described by saying that it is that combination of color which gives to the picture the effect of every object and part in it having been seen under the same conditions of atmosphere; having been seen at the same time, with the same modification, and with the same degree and quality of light vibration. Tone is _color value_ as distinguished from value as degree of power as light and shade; and in this is the perfection of subtlety of color feeling.
=Tone Painters and Colorists.=--Some painters have been called "tone painters," while others have been called "colorists;" not that tone painters are not colorists, but that there is a difference. It is a difference of aim, a difference of desire. Those painters who are usually called colorists, like Titian and Rubens, are in love with the richness and power of the color gamut. They are full of the splendor of color. They paint in full key, however balanced the canvas. Each note of color tells for its full power. Their stop is the open diapason, and their harmony is the harmony of large intervals and full chords.
The tone painter deals with close intervals. He is in love with subtle harmonies. What he loves is the essence of the color quality, and not its splendor. With the closest range he can give all possible half-tones and shades and modulations of color, yet never exceed the gray note perhaps; never once go to the full extent of his palette-power.
The utmost delicacy of perception and feeling, and the most perfect command of materials and of values, are necessary to such a painter. Above all, is he the "painter's painter," for the infinite subtlety and the exquisiteness of power are his. And yet this is the thing least appreciated by the lay mind, the most difficult to encompass, and requiring the most knowledge to appreciate.
=Scientific Color.=--To the scientist color is simply the irritation of the nerves of the retina of the eye by the waves of light. Different wave lengths give different color sensations. It is the generally accepted theory now that there are three primary sensations; that is, that the eye is sensitive to three kinds of color, and that all other shades and varieties of color are the results of mingling or overlapping of the waves which produce those three colors, and irritating more or less the nerves sensitive to each color simultaneously. These three primary colors are now stated to be red, blue, and _green_. The older idea was that they were red, blue, and _yellow_; and was based on experiments with pigments. Pigments do give these results; for a mixture of blue and yellow _pigment_ will give green, and a mixture of red and green _pigment_ will not give yellow, while the reverse is the fact with _light_.