1. A printer for printing based on calibration results in which a reference primary color ink is mixed with at least one additional primary color ink different from the reference primary color ink to approximate a predetermined target primary color, the printer comprising: an acquisition section configured to acquire spectral reflectance of the reference primary color ink printed on a base, spectral reflectance of the additional primary color ink printed on the base, and spectral reflectance of the base; a predicting section configured to calculate predicted spectral reflectance of a mixture of the reference primary color ink and the additional primary color ink by dividing a product of the spectral reflectance of the reference primary color ink and the spectral reflectance of the additional primary color ink acquired by the acquisition section by the spectral reflectance of the base raised to the power of a value obtained by subtracting 1 from a total number of the reference primary color ink and the additional primary color ink mixed together; an optimizing section configured to optimize an ink-amount set defining mixed amounts of the reference primary color ink and the additional primary color ink so that the predicted spectral reflectance of the mixture is approximated to spectral reflectance of the target primary color; and a printing unit configured to print in accordance with the ink-amount set optimized by the optimizing section.