In the present embodiment, in Step S150, the second relational equation is calculated while including the spectral reflectances or the characteristics-acquired gradation value in the reference. For example, in a case in which eleven gradation values in increments of 0.1 from the minimum gradation value (gradation value of 0) to the maximum gradation value (gradation value of 1) are the prediction target gradation values, the spectral reflectances of these eleven gradation values are obtained regarding the reference color, and only the gradation value of 0.5 is the characteristics-acquired gradation value, then a reference when creating a equation is differentiated between second relational equations corresponding to prediction target gradation values with gradation values of 0.5 or more and second relational equations corresponding to prediction target gradation values with gradation values of 0.5 or less. Specifically, each of the second relational equations corresponding to the prediction target gradation values of 0 or more and 0.5 or less is created with the spectral reflectances of the gradation value of 0.5 being taken as a first reference and with the spectral reflectances of the gradation value of 0 being taken as a second reference (see a portion A in FIG. 13), and each of the second relational equations corresponding to the prediction target gradation values of 0.5 or more and 1 or less is created with the spectral reflectances of the gradation value of 1 being taken as the first reference and with the spectral reflectances of the gradation value of 0.5 being taken as the second reference (see a portion B in FIG. 13). Note that, as the second relational equation for predicting the spectral reflectances of the gradation value of 0.5 for the prediction target color, a second relational equation created with the spectral reflectances of the gradation value of 0.5 being taken as the first reference and with the spectral reflectances of the gradation value of 0 being taken as the second reference may be adopted, or a second relational equation created with the spectral reflectances of the gradation value of 1 being taken as the first reference and with the spectral reflectances of the gradation value of 0.5 being taken as the second reference may be adopted. Moreover, the gradation value of 0.5 is the characteristics-acquired gradation value, and therefore, for the spectral reflectances of the gradation value of 0.5 for the prediction target color, actual measurement values may be directly applied thereto without using the second relational equation. Also for the spectral reflectances of the maximum gradation value (gradation value of 1) and the minimum gradation value (gradation value of 0) for the prediction target color, actual measurement values can also be directly applied thereto without using the second relational equations.