Color measurement Objective color evaluation performed by reflectance spectrophotometry allows the computation of CIE tristi- mulus values (X, Y, Z) which can be mathematically transformed into co-ordinates describing color in a more intuitive and easier way [26]. These co-ordinates determine lightness (L*in the CIE L* a* b* or Y in xyY system) and chromaticity (a*, b*in the CIE L* a* b* sys- tem; and xy in the xyY system).