1. An image processing apparatus provided in a host image forming apparatus amongst a plurality of image forming apparatuses, said image processing apparatus comprising: a color conversion part performing color conversion as between the host image forming apparatus and another one of the plurality of image forming apparatuses, including a first printer; a plurality of color profiles whereby colors of images formed by the host image forming apparatus may be made effectively approximate to those formed by other ones of the plurality of image forming apparatuses, through color conversion performed by said color conversion part with the use of the color profiles, said color conversion part using a color profile from amongst the color profiles provided in the host image forming apparatus to convert input color data, in a RGB color space, to converted color data, in a device-dependent RGB color space of said host image forming apparatus, for reproducing colors obtained by said first printer by applying said input color data, each of said input color data and said converted color data corresponding to a same color in a predetermined device-independent color space which does not depend on apparatus types; and a tone conversion part converting the converted RGB color data to converted CMYK data and forwarding the converted CMYK data to a printer engine of the host image forming apparatus, the printer engine reproducing the colors corresponding to the converted RGB color data by mixing or blending CMYK color materials, wherein the plurality of image forming apparatuses have respective different dither matrixes, wherein the color profile is generated by a process including: (a) producing, in a computer, color patch data by uniformly dividing a RGB color space; (b) obtaining color patches corresponding to the color patch data in an image formed by a first image forming apparatus of an apparatus type of said first printer; (c) measuring color of the color patches in the predetermined device-independent color space; (d) obtaining a relationship, for each color patch, between a first color space which depends on the apparatus type of the first printer and the predetermined device-independent color space, based on a measurement result of (c); (e) obtaining a relationship between the predetermined device-independent color space in an image formed by a second image forming apparatus of an apparatus type of said host image forming apparatus and a second color space which depends on said apparatus type of said host image forming apparatus; and (f) calculating a coordinate value in the second color space which depends on the apparatus type of said host image forming apparatus for each color patch whereby color of an image formed by said host image forming apparatus has a color difference which is effectively reduced from color of an image formed by said first printer, according to the relationship between the predetermined device-independent color space in an image formed by said host image forming apparatus and the second color space which depends on the apparatus type of said host image forming apparatus, obtained in (e), wherein color in an image formed by said host image forming apparatus using said device-dependent input color data is visually equal to color of an image formed by said first printer using said converted device-dependent color data.