The difference threshold of judging chromatic light was evaluated in this study. The experimental factors included target colour, background colour, interspacing, target surface interferences, and luminance level. Results showed that humans were more sensitive to green light than to red or blue light. The differential brightness sensitivity was higher for dark target on bright background than for bright target on dark background. The interspacing between two targets also affected differential brightness sensitivity, but the luminance level of the standard stimulus was found to have no effect on difference threshold. In addition, there was significant individual differences in differential brightness sensitivity. Further, by comparing the results obtained from the Analytic Hierarchy Process (AHP) and the method of constant stimuli, it suggests that the AHP approach was a valid and effective method to assess difference threshold.