Custom Color Printing refers to printing a customer-selected color as a solid area using a single toner or ink, rather than as a halftone of process colors. One example of custom color is the Pantone Color Matching System, containing ∼1000 precisely defined colors mixed from a set of 11 primary colors. Electrophotographic custom color printing requires mixing two or more colors from a set of primary toners and requires that the primaries have equal developabilities to prevent differential development and the resulting color shifts over long runs. Liquid toners meet the first of these requirements, but in a long run even very small differences in developability will lead to concentration changes in the toner supply and shifts in printed color. To compensate for those variations, the mixed toner in the developer housing can be replenished in a way that keeps printed color constant. In this paper we outline a differential replenishment method using feedback from various sensors. We describe in detail a simple close feedback loop control scheme that maintains color consistency throughout long print runs and also enables on-the-fly color changes. Applications for this technology include digital printing of black and one or two spot colors which is widely used in offset printing, e.g., packaging, forms, and event flyers.