Field trials of the nonlinear color-appearance model by Nayatani et al. were conducted by using the three chromatic-adaptation experiments by the Research Committee of CSAJ, Breneman, and McCann et al. Based on the preliminary analysis, the effective adaptation coefficient alpha(min) was introduced to the model to account for the effect of incomplete adaptation found under test chromatic illuminant. It was confirmed that the nonlinear color-appearance model combined with alpha(min) predicted quite nicely all the experiments. In addition, it was also found that the coefficient alpha(min) is different for different color stimuli (object color or photographic transparency). In addition, the value of alpha(min) changes by changing the adapting illuminance of the experiment in each of the two kinds of color stimuli used.