1. A colorimetric device for determining the colour of a surface-under-test (SUT) which, when illuminated, will produce at least diffusely reflected light, comprising: a housing including a wall having an aperture therein, interior surfaces of the housing being adapted to absorb light impinging thereon, the aperture to be covered by the SUT when the colorimeter is in use; light source means and photodetector means disposed in the housing and generally facing the aperture, the light source means being responsive to electrical drive signals for emitting light in at least three different spectral segments each encompassing a different band of wavelengths, the light source means being spaced apart so as to direct light of a particular said wavelength band towards the aperture from at least two directions, the photodetector means being disposed so as to receive said diffusely reflected light after reflection from said SUT covering the aperture; the colorimetric device further comprising: a drive unit for supplying said electrical drive signals to the light source means so as to cause them to emit said light of each of the three different wavelength bands and means for processing the corresponding electrical output signal from the photodetector means to provide three values each corresponding to a respective one of the three different wavelength bands, the drive unit and processing means being so configured that each of said values is distinct from the other values, the processing means being configured to derive from the at least three values a set of colorimetric coordinates identifying the colour of the SUT.