There exist individual differences in color matching functions and the use of a single standard observer as a representative of a whole population often limits the accuracy of color reproduction, especially for narrowband stimuli. We conducted a paired comparison experiment for 58 color-normal people involving color difference judgments using four nearly metameric spectra pairs. The performance of observer functions: CIEPO06, Sarkar's observers, and the extended CIEPO06 incorporating peak-shift in L and M cones were investigated. Large observer variability was found in the obtained results, which ismuch larger than what CIEPO06 predicts. At least two different groups were found in the experimental results, which could be explained by eye-lens and macular pigment optical density variations. We estimated the individual cone fundamentals from another experiment where observers performed five color matching, and used them to predict the paired comparison results. They gave better, or at least comparable prediction to those of CIE 1964 observer and CIEPO06.