1. A method for color adjustment by entering image data which expresses an input image in terms of color component value for a large number of pixels individually and then generating adjusted image data which expresses an adjusted image to be printed by a printing apparatus, with the input image color-adjusted, said method comprising: a step of outputting a preview image of said input image according to said image data and acquiring information about the unadjusted color which expresses the color to be adjusted and which is contained in said preview image; a step of controlling said printing apparatus such that it prints a plurality of colors among from the color and its neighboring colors represented by said information about unadjusted color, according to said information about unadjusted color which has been acquired; a step of specifying the information about adjusted color which represents any of the plurality of printed colors, as the standard information at the time of color adjustment; and a step of generating the data for adjusted image which expresses the adjusted image to be printed by said printing apparatus from said image data, according to said information about unadjusted color and said information about adjusted color.