Three experiments were carried out to investigate the change of perceived colour differences against backgrounds varying in lightness, hue and chroma, respectively. The results showed that the perceived colour difference was enhanced when the colours of the background and sample pair were close to each other, and the enhancement will be gradually weakened as the colour difference between them increases. However, this effect is different from the ‘crispening effect’ found by the previous studies which showed a very sharp increase of perceived colour difference when the background colour has the same colour of the pair considered. The results also showed that lightness background effect is larger than chroma and hue effects. The visual results were modeled for predicting the background effect