A method of defining color separation for printing an image, the method comprising: printing a representative set of Neugebauer Primary area coverage vectors (NPacs) for the printing system on a print medium, each NPac describing area coverages for a plurality of Neugebauer Primaries of an ink set used to print the representative set of NPacs; measuring the colorimetric value of the printed NPacs; selecting a plurality of NPacs from the printed representative set of NPacs based on the measured colorimetric value, wherein each selected NPac is to print a color corresponding to a point within an RGB cube, wherein the method comprises: (i) selecting an initial set of eight of a representative set of NPacs corresponding to the vertices of an RGB cube; (ii) computing a tetrahedral RGB tessellation and mapping the tetrahedral tessellation to the initial set of NPacs in the NPac-related color space; (iii) determining whether any of the tetrahedra in the NPac-related color space overlap and/or have volume discrepancies greater than a predetermined amount; (iv) in the event that any of the tetrahedra in the NPac-related space overlap and/or have volume discrepancies greater than a predetermined amount, selecting a revised set of eight of the representative set of NPacs corresponding to the vertices of an RGB cube, and repeating steps (ii)-(iv) until a set of eight of the NPacs result in none of the tetrahedra in the NPac-related space overlapping and none of the tetrahedra having volume discrepancies greater than the predetermined amount; and defining color separation for use in printing a color image based on the selected NPacs. printing a representative set of Neugebauer Primary area coverage vectors (NPacs) for the printing system on a print medium, each NPac describing area coverages for a plurality of Neugebauer Primaries of an ink set used to print the representative set of NPacs; measuring the colorimetric value of the printed NPacs; selecting a plurality of NPacs from the printed representative set of NPacs based on the measured colorimetric value, wherein each selected NPac is to print a color corresponding to a point within an RGB cube, wherein the method comprises: (i) selecting an initial set of eight of a representative set of NPacs corresponding to the vertices of an RGB cube; (ii) computing a tetrahedral RGB tessellation and mapping the tetrahedral tessellation to the initial set of NPacs in the NPac-related color space; (iii) determining whether any of the tetrahedra in the NPac-related color space overlap and/or have volume discrepancies greater than a predetermined amount; (iv) in the event that any of the tetrahedra in the NPac-related space overlap and/or have volume discrepancies greater than a predetermined amount, selecting a revised set of eight of the representative set of NPacs corresponding to the vertices of an RGB cube, and repeating steps (ii)-(iv) until a set of eight of the NPacs result in none of the tetrahedra in the NPac-related space overlapping and none of the tetrahedra having volume discrepancies greater than the predetermined amount; and measuring the colorimetric value of the printed NPacs; selecting a plurality of NPacs from the printed representative set of NPacs based on the measured colorimetric value, wherein each selected NPac is to print a color corresponding to a point within an RGB cube, (i) selecting an initial set of eight of a representative set of NPacs corresponding to the vertices of an RGB cube; (ii) computing a tetrahedral RGB tessellation and mapping the tetrahedral tessellation to the initial set of NPacs in the NPac-related color space; (iii) determining whether any of the tetrahedra in the NPac-related color space overlap and/or have volume discrepancies greater than a predetermined amount; (iv) in the event that any of the tetrahedra in the NPac-related space overlap and/or have volume discrepancies greater than a predetermined amount, selecting a revised set of eight of the representative set of NPacs corresponding to the vertices of an RGB cube, and repeating steps (ii)-(iv) until a set of eight of the NPacs result in none of the tetrahedra in the NPac-related space overlapping and none of the tetrahedra having volume discrepancies greater than the predetermined amount; and defining color separation for use in printing a color image based on the selected NPacs.