A method for determining color-matching functions includes obtaining spectral data originating from metameric pairs and generating new color matching functions by modifying original color matching functions. The new color matching functions are constrained to be similar to the original color matching functions while reducing calculated perceptual error between the metameric pairs. In another embodiment a method for determining color-matching functions spectral data originating from color matching experiments and from metameric pairs are generated. Color matching functions from a set of parameters and an error function that indicates error due to perceptual differences between the parameterized color matching functions and the color matching experiments are defined. Methods for defining human observer functions, optimizing the definitions of LMS cone response functions as well as other methods and systems are also disclosed.