Criminal Psychology: A Manual for Judges, Practitioners,...

Concerning color vision only a few facts will be mentioned: 1. It will be worth while, first of all, to consider whether color exists. Liebmann holds that if all the people were blind to red, red would not exist; red, i.e., is some cervical phantasy. So are light, sound, warmth, taste, etc. With other senses we have another world. According to Helmholtz, it is senseless to ask whether cinnabar is red as we see it or is only so as an optical illusion. “The sensation of red is the normal reaction of normally constructed eyes to light reflected from cinnabar. A person blind to red, will see cinnabar as black, or a dark grayish yellow, and this is the correct reaction for these abnormal eyes. But he needs to know that his eyes are different from those of other people. In itself the sensation is neither more correct nor less correct than any other even though those who can see red are in the great majority. The red color of cinnabar exists as such only in so far as there are eyes which are similar to those of the majority of mankind. As such light reflected from cinnabar may not properly be called red; it is red only for especial kinds of eyes.” This is so unconditionally incorrect that an impartial judge of photography says[179] that everything that normal eyes call violet and blue, is very bright, and everything they call green and red is very dark. The red-blind person will see as equal certain natural reds, greens and gray-yellows, both in intensity and shadow.

But on the photograph he will be able to distinguish the differences in brightness caused by these three otherwise identical colors. We may, therefore, assume that colors possess objective differences, and that these objective differences are perceived even by persons of normal vision. But whether I am able to sense the same effect in red that another senses, and whether I should not call red blue, if I had the color-vision of another, is as impossible to discover as it is useless. When the question of color is raised, therefore, we will try to discover only whether the person in question has normal color-vision, or what the nature and degree of his abnormality may be.

2. It is not unimportant to know whether single tints are recognizable in the distance. There have been several examinations of this fact. Aubert[180] constructed double squares of ten millimeters and determined the angle of vision at which the color as such could be seen. His results were:

It is interesting to notice that the angle for blue on a white background is almost nine times that for white, orange, or yellow on a black background. In cases where colors are of importance, therefore, it will be necessary to discover the color and the nature of its background before the accuracy of the witness can be established.

3. It is well known that in the diminution of brightnesses red disappears before blue, and that at night, when all colors have disappeared, the blue of heaven is still visible. So if anybody asserts that he has been able to see the blue of a man’s coat but not his red-brown trousers, his statement is possibly true, while the converse would be untrue. But there are no reliable or consonant accounts of the order in which colors disappear in increasing darkness. The knowledge of this order would help a great deal in the administration of criminal justice.