This paper describes a method for scoring the Farnsworth-Munsell 100-Hue test, based on maximum-likelihood estimation, which in theory reduces test-to-test variability in scores and which is therefore better able to discriminate between different levels of overall colour discrimination than is the original Farnsworth scoring system. Error scores produced by the method are directly comparable to error scores produced by the traditional scoring system. It is hoped that this work will provoke further consideration of the efficiency of the scoring system as far as test-to-test variability is concerned, including the efficient detection of polarity in the subject's hue discrimination function.