1. A method of calibrating the half-tone operation of a color marking engine for creating half-tone images formed in bi-level or quad-level dot density formats, comprising the steps of: running a test pattern on each of one or more color marking engines to provide an output image of a plurality of gray patches formed of first, second and third color toners associated with the color marking engine wherein the gray patches include first, second and third sets of patches reproduced respectively at dot density levels of 25%, 50% and 75% of a maximum dot density and wherein relative color toner levels in the gray patches within each first, second and third set of patches vary a predetermined increment in value above or below the toner levels in a median valued gray patch; visually selecting an output image of a selected color marking engine having a minimum of color shift associated therewith in accordance with predetermined visual criteria; determining a correction factor defined for each color at the maximum dot density; and storing the correction factor as an offset maximum density for images created at the bi-level and quad-level formats.