The final and most intriguing results concerned the effect that prior knowledge or memory of an object has upon the categorization or perception of its colour. The hues were now presented within the outlines of fruit and vegtables. The results suggested that the expectation of the fruit's colour heavily biased the categorisation in the direction the colour expected. For example, many more test hues were categorised as yellow when presented within the outline of a banana than if presented in a circular patch.

This finding was further investigated in a colour adjustment paradigm. The subject was presented with a target patch and asked to adjust the colour to mean grey. The target patch was either in the shape of a fruit or one of several control conditions. The subject was also asked to adjust the colour to match the typical colour of the presented fruit or vegetable outline. Typical findings are shown in figure 3. Remarkably the colours that are judged to be grey by the subjects are in fact shifted well away from the true achromatic point, in the opposite direction the fruit's typical colour in colour contrast space. The memory, and therefore expectation of the typical colour of the fruit has strongly biased the subjective categorisation of grey.

Figure 4 shows how the results hold for all the fruit and vegetables tested, with the possible exception grapes where the typical colour is, of course, ambiguous. From these results Professor Gegenfurtner concluded that photographs of fruits and vegetables are perceived in the characteristic color of the object if the average color of the pixels in each photo is grey. For the objects to appear grey, subjects adjusted the average color 10% - 30% in the colour direction opposite to the remembered colour.

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