Several passive and active banding compensation strategies have been proposed in recent literatures for monochrome EP processes. In these studies, quasi-periodic contrast variations can be effectively reduced. For polychrome EP process, in which multiple color layers are superimposed on top of one another, Klassen and Goodman have shown the dependence of contrast sensitivity on variation in chromatic channels such as a* and b*. Chromatic bandings are quasi-periodic gratings with variation in chromatic channels. Chromatic banding may still be perceivable when the achromatic banding on individual color layers has been reduced to under the threshold. The perceptibility of chromatic banding is dependent on the primary colors of the platform. Before a softcopy psychophysics experiment was conducted, a set of tone curves and a model of the mixing of two primary colors, excluding the black, were constructed according to a 4-color EP printer. The psychophysics study confirmed that even if the sinusoidal gratings (in L*) on each individual primary color layer is under the human visual system (HVS) threshold, superimposing one on top of another can increase the perceptibility of the composite gratings. These results will be much valuable to ongoing efforts to reduce chromatic banding.