Next, a relational equation which represents the relationship between the spectral reflectances of the maximum gradation value and the spectral reflectances of the prediction target gradation value for the reference color is obtained (Step S150). The relational equation will be hereinafter referred to as a “second relational equation.” Note that, herein, it is assumed that eleven gradation values in 0.1 increments from the gradation value of 0 to the gradation value of 1 are the prediction target gradation values. A specific method for obtaining the second relational equation is the same as the method for obtaining the first relational equation. The second relational equation is obtained for each of the prediction target gradation values, and therefore, eleven second relational equations are obtained herein.

Finally, using the second relational equation, the prediction values of the spectral reflectances of the prediction target gradation value for the prediction target color are obtained (Step S160). Specifically, the spectral reflectances of the maximum gradation value for the prediction target color are applied to the second relational equation obtained in Step S150, whereby the prediction values of the spectral reflectances of the prediction target gradation value for the prediction target color are obtained. Herein, the number of prediction target gradation values is eleven, and therefore, the spectral reflectances of the maximum gradation value for the prediction target color are applied to the eleven second relational equations. Thus, for the prediction target color, the prediction values of the spectral reflectances of each of the eleven prediction target gradation values are obtained.