1. A subtractive color method comprising: a first step of obtaining a most used color that is a most popularly used color in a first image having a predetermined size; a second step of extracting, as first pixel groups, pixel groups formed of continued pixels having an identical color other than the most used color in the first image; a third step of extracting, as third pixel groups from among the first pixel groups thus extracted, pixel groups having a color of which a color difference with respect to the most used color is smaller than a predetermined threshold value and having a size thereof that is smaller than a predetermined size; and a fourth step of generating a resultant image by: defining, as second pixel groups, the first pixel groups other than the third pixel groups; obtaining an image, as a second image, having an area identical with that of the first image and filled with the most used color; and replacing portions, in the second image, corresponding to the second pixel groups with the second pixel groups, respectively, so that the resultant image, based on the second image, has the portions of which colors are replaced with colors of the corresponding second pixel groups, respectively.