A color-processing method includes: selecting a target color gamut to produce an input color signal; calculating a mixture ratio enabling primary colors of the target color gamut to be created by mixing primary colors of a color gamut of the color reproduction apparatus to reproduce the input color signal therewith; producing primary colors reconfigured by mixing the primary colors of the color gamut of the color reproduction apparatus according to the calculated mixture ratio; adjusting an illuminant to match an output signal to a color gamut determined by the reconfigured primary colors; and converting the input color signal to match to the primary colors determined by the reconfigured primary colors. Further a user can arbitrarily set a color gamut in a range that a color reproduction apparatus can reproduce regardless of an input color signal without a quantization errors.