This experiment was carried out to investigate some viewing parameters affecting perceived colour differences. It was divided into eight phases. Each phase was conducted under a different set of experimental conditions including separations, neutral backgrounds, and psychophysical methods. Seventy-Jive wool sample pairs were prepared corresponding to five CIE colour centers. The mean colour difference was three CIELAB units. Each pair was assessed by a panel of 21 observers using both the gray scale and pair comparison psychophysical methods. The assessments were carried out using the three different back grounds (white, mid-gray, and black) and a hairline gap between the samples. Assessments on the gray background were repeated using a large (3-inch) gap between the samples. It was found that the visual results obtained from both psychophysical methods gave very similar results. The parametric effect was small, i.e., the largest effect was only 14% between the white and gray background conditions. These visual data were also used to test four colour-difference formulae: CIELAB, CMC, BFD, and CIE94. The results showed that three advanced colour-difference formulae performed much better than CIELAB. There was a good agreement between the current results and those from earlier studies.