Popular Science Monthly/Volume 55/June 1899/The Sense of Color

First published as "Sur le sens de la couleur" in Revue Scientifique, 26 February 1898. pp.270-271. Author's name given as André Brocchi.



WHEN the different rays of the solar spectrum strike the eye separately they each produce a particular characteristic and subjective impression, which is called color. Ingenious theories have been set forth by physiologists, like Young, Helmholtz, Hering, and others, to explain the perception of colors by our eye, but the problem still awaits solution, and is not likely to be explained from that side, because it is rather psychical. The laws regulating the perception of colors are not physiological; we perceive only relations. We know that the sense of color may be modified independently of that of light and of space. Two phases may be distinguished in its evolution. Every light, whether chromatic or not, produces a simple luminous impression on the retina—a simple excitation of the optic nerve, without being analyzed by it. In the second phase the brain, the psychic center of color, intervenes. There may obviously be considerable differences between persons in the interpretation of what we call colors, and we may judge that there is an education of this psychical center, and that it is an important matter.

Different as the ways of interpreting a sensation of color may be, there are still some fundamental ideas in the matter which painters, for example, do not all observe. Some, like the impressionists, exaggerate them, and others neglect them. Which of these are wrong? and which right? are questions we are not concerned with, our purpose being to show that many of the phenomena of color, shade, sources of light, etc., escape a large proportion of persons unless they are attentive observers. If we visit the exhibitions of the impressionists we shall be entertained at the criticisms we hear over the canvases of such painters as Renoir and Monet; youths who have just come out of the drawing school declaring that their master never taught them to put blue on a face, and that in Nature all shadows are gray or black, and none red or violet; and we should astonish a great many people if we should say that a white robe should never be painted in a portrait picture with white lead alone. "All skies are blue, all trees are green, all pantaloons are red," said a celebrated painter who was trying to show how the habit of seeing a colored object in a certain way prevented one from perceiving the different colors that might be applied to it. We recollect the trouble of a brave youth who, having sat for his portrait to a celebrated painter, was distracted at perceiving green in the reflections of the hair of his likeness. Yet there are in Nature shadows that are blue and reflections that are green, and if we do not see them habitually it is because we do not give sufficient attention to them.

A common division of the spectrum is into warm and cold colors. The warm colors are red, yellow, orange, and yellow-green; the cold colors are violet, blue, green, and blue-green. This is not an arbitrary division, but answers to a fact of experience which passes from our physical to our moral impressions, and may cause in us feelings of comfort or uneasiness, joy, sadness, or moral depression. Some persons are influenced by the gray-colored sky, others are gay when the day is bright. It is a current expression that the color of the southern landscape is warm. Goethe said that blue caused him to feel cold.

The terms warm and cold are technical expressions in the arts. A color tone is cooled by putting blue in it, and warmed by adding red or yellow. "This practice is not arbitrary," says M. F. Bracquemond in his book on Design and Color; "it copies the colored aspects which natural light imposes on all imitation that seeks to realize the colored and factitious light of painting. To reach this, art observes the order according to which the natural lights distribute their various colored elements, and classes luminous aspects—a process which it has always observed—into the two categories of warm and cold. Hence, so far as examples come to us, this contrast is easy to verify; at the Louvre, for example, in works from Pompeii, and in those of all the masters." Preyer relies upon this division of colors into warm and cold for a comparison of chromatic sensations with thermic, and for supposing that the color sense is developed from the sense of temperature. Chromatic sensitiveness to this author is only a special case of thermic sensitiveness limited to the retina. Darwin's ideas were evidently the same; the whole human body was a sort of retina capable of improvement; we may, it is true, suppose with Lord Kelvin that "there is absolute continuity between the perception of heat by the retina of the eye and its perception by means of the tissues and nerves."

A very elementary experiment will easily enable us to recognize these different qualities of colors. Set a lighted candle on a table near a window; there are then two sources of light—the daylight, blue and cold, and the light of the candle, orange-red and warm. Cast a shadow on the white paper by holding a pencil straight up. The shadows cast by the candle will be blue to a degree that no one can mistake it, a greenish blue. Placing the pencil between the window and the candle and looking at the shadows, we have, first, the blue shadow of the candle, and then the shadow projected by the cold daylight. The color of the last, though perhaps less evident than the other, is an orange-yellow, of rich, warm tone.

From this little experiment we may conclude that a warm light provokes a cold shadow, a cold light a warm shadow, and that the color of the shadow is complementary to that of the light. In the experiment, daylight was the source of the cold light. Let us now take a third source of light, warmer than that of the candle, the flame produced by burning alcohol and salt—a very warm, deep orange light, which makes the light of the candle seem cold and its blue shadows appear yellow, while its own shadows are blue.

We recently observed a very striking example of these warm and cold appearances of light; it was at the theater: a beam of red light shone brightly upon an actor, whose shadow was absolutely green. Some of the people around us were astonished at the phenomenon, which they could perceive very plainly. Phenomena of this kind are produced every instant in a nature illuminated by the sun; nearly all the shadows are colored in hues which we can distinguish with a little attention where the unpracticed eye sees nothing but gray. Thus in a mountainous country, exposed to the warm light of the sun, the mountains in the horizon appear blue through the haze; then, as evening draws on, the sun appears a deeper orange, more reddish, while the sky seems green by contrast, and the red rays of the sun falling on the mountains turn them violet, in those beautiful tints which give so much glory to those countries of large shadows and bright lights.

However intense the light of day may be, it is therefore always colored, and gives those colored shadows which painters do not always observe. The painter, in fact, should make an analysis of the complex light around him, and should repeat the result in synthesis on his canvas. Upon hardly any other condition can he represent the transparency of the atmosphere, or the luminosity of a subject or a landscape. These colored shadows are not, therefore, false colors, as often seems to be believed, or optical illusions; they are really existent, but our eyes are hardly ever practiced enough to discern them; we are deficient in education of the color sense. This education is not hard to attain. There are persons who have special aptitudes and are consequently remarkable colorists, just as some persons have an admirably organized ear for music; but, besides these, it is possible for all persons endowed with the faculty of observing and capable of attention to acquire with considerable rapidity the faculty of discerning colors, where they at present hardly see anything but confused gray masses. (The epithet gray, we may observe, is used as applied to many things the color of which is not susceptible of exact determination.) Such attentive observation of colors is, however, attended with some danger to painters. Every person prefers some one color, is influenced by a particular shade. When we examine the works of the painters we see that there are many differences in the way of seeing. Some see blue, red, green; others see clear, others obscure. In the analysis of a complex color it happens that there is sometimes an auto-suggestion. Where there is a hardly defined violet, the painter will exaggerate it on his canvas, and will be obliged, in order to keep up the right tone, to increase the intensity of the colors next to it. Hence arises a common error with painters, who start with a true principle, but are not able to apply it properly, and give their picture a tonic violet, green, or yellow, beyond all reason.—Translated for the Popular Science Monthly from the Revue Scientifique.