In web-fed, multicolor printing operations wherein individual colors which make up the final composite copy are separately applied to the web, each at a separate printing unit or station, the invention provides a new and advantageous method of controlling the color densities and tones obtained in said composite copy, so that they closely correspond to those of the original art work or composition to be reproduced. The method provided employs electrical energy of controlled relatively high voltage and low amperage which is applied in the area of each printing unit or station wherein said individual colors are transferred to the web, whereby to effect or assist said transfer. It further provides for separately regulating the potential of the electrical energy supplied to each of the separate printing units or stations, to govern the amount of pigment there transferred to the web and thereby independently control the density of each individual color in the composite copy. By controlling the density of each individual color applied to the web, the tone values of combined colors in the copy (such as, for example, a purple formed by overprinting blue on red) may also be controlled.