Background is one of the important factors that affect colour appearance of samples. In general, a background colour induces colour appearance of a sample to shift towards the complementary colour of the background. For example, grey on black background appears lighter than the same grey on white background. Shape of colour sample is also a factor that can affect sense and mood of observers. The degree of colour shifts due to the background colour might be different for different shapes of colour samples. This study thus investigated this aspect. In visual experiments, the observers were 40 Thais, 20 women and 20 men, with an average age of 24.3 years, all with normal colour vision. Each observer matched colour appearance of square samples presented on a grey background with that of test samples with different shapes on a chromatic background. Six shapes, i.e. circle, square, diamond, isosceles triangle, right-angled triangle and hexagon, and four chromatic backgrounds, i.e. red, green, yellow and blue, were investigated. The differences between colours of the test and the matching samples were quantified by CIE total colour difference, ∆E*[subscript ab]. It was found that circle induced the most changes in colour appearance of the sample due to the influence of background colour and diamond showed the minimum induction. Both shape and background contributed to changes in colour appearance