The variability in correlating visual colour discrimination with colorimetric measures may be understood better if parameters that affect the correlation are quantified. A review is given of known parametric effects of a human and physical nature, and advice is given for a tentative modification of colour-difference evaluation techniques based on characterized parametric effects. >p> Human factors such as variability in and between observers are very important random factors, and may be a major source of uncertainty. Some physical changes in the presentation of colour-discrimination tasks are shown to produce significant shifts of colour-difference sensitivity. In some cases these changes have been quantified, however, these results were carried out using quite different experimental techniques (such as colour matching using a visual colorimeter or judgements of constant stimuli using physical samples) and are based upon very limited numbers of colour centres and observations. Hence, more research is needed for a full understanding of their influence.

The report contains 18 pages, 1 figure and 3 tables.