Colour reproduction methods of today do not try to reproduce the original spectral distribution of the original colours. Instead, they make use of the fact that the eye and the brain perceive colour via three sensitivity functions. In order to get correct colour mpression, it is therefore sufficient that the reproduced colour gives the same response in the brain as the original colour. However, an important limitation with this method is that it is only valid for a given viewing condition. If the viewing situation is changed (for example if the light source is changed from daylight to indoor illumination), there is a large risk that the colours are perceived differently, this phenomenon is known as metamerism. Furthermore, colour control systems of today rely on physical colour measurements, which make the colour reproduction valid only when the viewing conditions coincide with the colour measurement setup. In practice this is seldom the case. These limitations give large problems for applications that put high demands on correct colour reproduction. Examples of such applications are proof printing and high quality packages and catalogues.