A process for grading the colour of a diamond which is operable using a computerized system, wherein the colour of the diamond is correlated with the colour of a diamond of a plurality of diamonds each having a colour grading assigned thereto, the computerized system including an optical image acquisition device, a processor module and an output module operably interconnected together, said process including the steps of: (i) acquiring via an optical image acquisition device at least a first optical image of the table of a diamond, wherein the first optical image is acquired at a predetermined angle of with respect to the central axis extending normal to the table and through the apex of the pavilion of the diamond and in a direction of towards the table and characterised in that the first optical image is acquired when the diamond is located at an aperture interconnecting each sphere of a pair of integrating spheres of an integrating sphere system, wherein a light source is provided in each of the spheres providing an environment having a predetermined constant light level; (ii) in a processor module comparing data derived from acquisition of the at least a first optical image with a plurality of data sets each of which corresponds to a diamond of a plurality of diamonds, wherein data sets are each derived from an optical image of the table of the plurality of diamonds acquired by an optical image acquisition device in an environment having a predetermined constant light the same as that as (i) and each of the data sets is assigned a colour grading, and wherein said data derived from acquisition of the at least a first optical image and the data of said data sets are data indicative of the colour of the diamond from which it is acquired; and (iii) from an output module, responsive to a predetermined threshold of correlation between the data derived from input of the first optical image and the data of one of the plurality of data sets from step (ii), an output signal is provided indicative of the colour grade of the diamond. (i) acquiring via an optical image acquisition device at least a first optical image of the table of a diamond, wherein the first optical image is acquired at a predetermined angle of with respect to the central axis extending normal to the table and through the apex of the pavilion of the diamond and in a direction of towards the table and characterised in that the first optical image is acquired when the diamond is located at an aperture interconnecting each sphere of a pair of integrating spheres of an integrating sphere system, wherein a light source is provided in each of the spheres providing an environment having a predetermined constant light level; (ii) in a processor module comparing data derived from acquisition of the at least a first optical image with a plurality of data sets each of which corresponds to a diamond of a plurality of diamonds, wherein data sets are each derived from an optical image of the table of the plurality of diamonds acquired by an optical image acquisition device in an environment having a predetermined constant light the same as that as (i) and each of the data sets is assigned a colour grading, and wherein said data derived from acquisition of the at least a first optical image and the data of said data sets are data indicative of the colour of the diamond from which it is acquired; and (iii) from an output module, responsive to a predetermined threshold of correlation between the data derived from input of the first optical image and the data of one of the plurality of data sets from step (ii), an output signal is provided indicative of the colour grade of the diamond.