1. A method of searching for colour images stored in data storage means using a control unit, the method comprising: inputting a query relating to colour of an image, comparing, using the control unit, said query with descriptors for stored images derived in accordance with a method that includes: representing a colour image comprising two or more colours as dominant colours for an image and, for each dominant colour, calculating variance of colour distribution of the image in colour space relative to the dominant colour, representing the image in terms of colour space value of each dominant colour and value of respective colour variance; and forming a descriptor including the color space value of each dominant colour and the respective colour variance value; and using a matching function and selecting and displaying, using the control unit, at least one image for which the matching function indicates a close match between the query and at least part of the image, wherein the matching function is based on D ⁢ ⁢ ( F 1 , F 2 ) = ∑ j = 1 N 1 ⁢ ⁢ ∑ i = 1 N 1 ⁢ ⁢ p 1 ⁢ i ⁢ p 1 ⁢ j ⁢ f 1 ⁢ i ⁢ ⁢ 1 ⁢ j + ∑ i = 1 N 2 ⁢ ⁢ ∑ j = 1 N 2 ⁢ ⁢ p 2 ⁢ i ⁢ p 2 ⁢ j ⁢ f 2 ⁢ i ⁢ ⁢ 2 ⁢ ⁢ j - ∑ i = 1 N 1 ⁢ ⁢ ∑ j = 1 N 2 ⁢ ⁢ 2 ⁢ p 1 ⁢ i ⁢ p 2 ⁢ j ⁢ f 1 ⁢ i ⁢ ⁢ 2 ⁢ j , ⁢ where f xiyj = 1 2 ⁢ π ⁢ v xiyjl ⁢ ⁢ v xiyju ⁢ ⁢ v xiyjv ⁢ exp ⁢ [ - ( c xiyjl v xiyjl + c xiyju v xiyju + c xiyjv v xiyjv ) / 2 ] ⁢ and c xiyjl = ( c xil - c yjl ) 2 , v xiyjl = ( v xil + v yjl ) , ⁢ c xiyju = ( c xiu - c yju ) 2 , v xiyju = ( v xiu + v yju ) , ⁢ c xiyjv = ( c xiv - c yjv ) 2 , v xiyjv = ( v xiv + v yjv ). where D is the similarity measure; F 1 represents the first descriptor; F 2 represents the second descriptor; i and j index the representative colours; x and y index the descriptors; N 1 is the number of dominant colours in the first descriptor; N 2 is the number of dominant colours in the second descriptor; P 1i is the ith weight in the first descriptor; P 2j is the jth weight in the second descriptor; l, u and v represent colour components; and c and v are the dominant colour values (mean values) and variances respectively.