The literature is very contradictory concerning names for people with different types of abnormal color vision. The problem is primarily due to the ancient interest in the subject and the use of ambiguous generic names beginning in the 19th Century. This work attempts to use the generic names to the greatest extent possible to avoid confusion. This frequently requires the introduction of prefixes or modifying phrases as seen in the table below.

This table, from Chapter 18 of PROCESSES IN ANIMAL VISION, presents all of the possible types of abnormal color vision in a hierarchal form. It begins with the subject with normal color vision and ends with a totally blind subject. Between these two extremes are two major groups; those exhibiting anomalous properties and those exhibiting a total failure in one or more circuit elements of the visual system. The first are the anomalous trichromats and the second are the incomplete trichromats.

Historically a dichromat has been defined, based on observation of his performance, as a subject that could match any color using only two colors of variable intensity. Unfortunately, this is not an exclusive definition. All normal trichromats can match any color using only two colors of variable intensity. The two colors just need to be selected more carefully. In this work, a dichromat is defined based on his number of functional spectral photodetection channels. Thus, a monochromat has only one functional spectral channel. An achromat cannot perceive color but all three of his spectral photodetection channels are fully functional.

Under the old performance based definition, all of the classes shown in the upper left shaded box were considered dichromats and all of the classes shown in the lower right shaded box were considered monochromats. Both of these boxes contain both with apples and oranges.

Using the above new nomenclature, it is possible to describe a subject with abnormal color vision much more precisely. As examples, unique New CHROMATICITY DIAGRAMS are presented for both the Deutranope and the Tetartanope. These figures answer the age old question: "What does a color blind person see?"

Also available are much more precise interpretations of readings taken with the Nagel Anomaloscope.