Pseudo-isochromatic plates with varying background lightness were used in a display-based colour vision experiment. As in previous work, the background was found to have a small effect on the ability of observers to identify the patterns on the plates. The time taken to recognize the patterns was significantly affected for both colour-normal and colour vision deficient observers, with darker backgrounds associated with shorter response times and white backgrounds having the longest response times, suggesting a greater degree of task difficulty. Possible reasons for the results when test plates were presented with a white background are suggested, including lower apparent colourfulness and greater difficulty in visual integration of the figure.