The study of colour-blindness has been
somewhat retarded by the concomitant study of colour
theories. The majority of investigators have started
out unduly biased by their favourite theory and have examined colour-blinds from this prejudiced standpoint.
The result is that great deal of unnecessary
confusion has gathered round this subject which has
ultimately caused an obscuring of the real issues.
Attempts have been made from time to time to get from
theories but on the whole these have proved futile
and the results achieved are only gradually permeating
the literature of the subject. Yet even in the highest authoritative references to colour-blindness, it is amazing to find that a description of the defect is inevitably given along the lines of some particular theory, although it must be admitted that some authors take the precaution of inserting a note to the effect that such a description holds only if the theory be accepted.