An interactive tool was developed for modifying the colour appearance of pictorial images displayed on a monitor, whereby this was done by altering the colours of their pixels depending on the region of colour space into which they belonged. Using this tool, eleven observers took part in the experiments in which they modified the colours of four images processed through a gamut mapping algorithm. Observers first inspected which part of the reproduction image gave the most unsatisfactory match, then selected the corresponding region of CIELAB, and finally adjusted the image pixels from that region. Data analysis was then carried out to compare the original and reproduced images by generating various plots.