1. A color adjustment method for obtaining a coefficient for performing color conversion of input color space into output color space with respect to a predetermined adjustment object region within color space to which a color image belongs, the color adjustment method comprising: obtaining a coefficient for converting a color within the adjustment object region into another color on the output color space, which is the same color space as the input color space, with maintaining continuity of gradations and not causing color inversion within the adjustment object region, wherein the adjustment object region includes: movement source partial color space including a color, which is an object of processing of the color conversion; and movement destination partial color space including a color corresponding to the obtained coefficient.