Color-blindness is an abnormal condition of the visual apparatus, causing an inability to accurately, invariably and properly distinguish the colors of the solar spectrum. Several varieties exist, but the most frequent is that causing difficulty or impossibility in distinguishing between red and green, which is especially unfortunate, as these colors are universally adopted as important signals in transportation service.
Investigations indicate the universality of chromatic aberration in all observed nations, but with diminished frequency in the educated, and in peoples possessing great love for colors and artistic decorations such as the Africans, Japanese and Chinese. Indeed, it is claimed by some observers that the people of India are able to perceive 300 different shades of colors not perceptible to European eyes.
No evident physical manifestation exists rendering an objective diagnosis possible. Opinions as to color visual acuity must therefore rest on tests, which are well described in text-books.