Previous research has shown the effects of hue and ligtness on judgments of perceived size. Findings are that red stimuli appear larger than blue ones, and that lighter stimuli seem to ba larger than darker ones. Applicability, of these results in product or interface design is limited, since the size-effect of colour has nor been studied in relation to the user＇s task. In this article, the effect of colour on perceived fit between objects is studied in a puzzle task. Subjects are asked to select a peg fitting to a hole. The response merle is varied by pointing or actually handling the pegs, feedback being only available in the latter condition. A comparison between colour appearance is made by using surface (real puzzle) and self-luminous colours (computer screen). The hypotheses are that red pegs that are too small are chosen more often than blue ones, and that lighter coloured pegs that are too small are chosen more often than darker pegs. In the real puzzle task, perceived fit is not influenced by hue but is influenced by brightness when rising a fluorescent colour. Hypotheses on the effects of hue and brightness are both confirmed when judging self-luminous colours on a computer screen.