1. A method of determining a reflectance spectrum, comprising: obtaining a normalized value from a plurality of illuminant sensor outputs, each illuminant sensor output indicating a reflectance value obtained from a target; obtaining reference data from a reference database comprising training samples that correlate reference spectra with a corresponding plurality of normalized illuminant sensor outputs for reference colors, the reference database comprising a plurality of clusters, each cluster having a cluster centroid, each one of the training samples being associated with one of the clusters; determining, for each plurality of illuminant sensor outputs, a Euclidean distance to each cluster centroid; identifying a most appropriate cluster based on the Euclidean distances, the most appropriate cluster being the cluster corresponding to the shortest Euclidean distance; and determining a spectrum based on the illuminant sensor outputs and only the reference data from the most appropriate cluster.