A method for adjusting fractional amounts of primary colors to be combined to substantially match a user selected color and substrate characteristics in a device adapted to color printing on a substrate. The method corrects for both the color and the reflectivity of the substrate on which the user selected color is to be printed. The method adjusts the target mixed ink transmission spectrum to compensate for the substrate characteristics. The method also identifies cases in which the target mixed ink transmission spectrum may not be compensated due to the paper's color. The method may be used to control mixing of inks in a custom color module of a marking engine; or mixing of dry toner primaries in a dry xerographic engine; or mixing of printing inks in a stand-alone ink mixing station.