1. A color-conversion-table creating method comprising: (a) defining a color gamut in a first color space defined for a first device, the color gamut having a surface, an internal space surrounded by the surface, surface grid points positioned on the surface, and internal grid points positioned in the internal space; and determining a correspondence relationship between the surface grid points in the first color space and parameters in a second color space defined for a second device; (b) determining, based on the correspondence relationship determined in step (a), a correspondence relationship between the internal grid points in the first color space and parameters in the second color space; and (c) creating a color conversion table indicative of a correspondence relationship between all grid points in the first color space and parameters in the second color space based on both the correspondence relationship determined in step (a) and the correspondence relationship determined in step (b), the all grid points including the surface grid points and the internal grid points, allowing the color conversion table to be used for converting image data represented in the first color space into image data represented in the second color space.