An apparatus and associated method for varying the color and/or flavor of an extruded food product during a single production run of a single extrusion device. The apparatus includes a mufti-additive injection system, which is attached to a fluid supply line of an extrusion device. The injection system is comprised of a plurality of additive supply tanks, which are each in fluid communication with the fluid supply line via an injection manifold, and a metering mechanism which selectively controls the amount of additive injected into the supply line by each individual supply tank. The injection system may also include a central control mechanism for calibrating the amount of additive injected into the supply line and for maintaining a constant fluid volume added to the extrusion device. Each of the additive supply tanks may contain a different colorant and/or flavoring. Two variants of the injection manifold are provided as well as a novel injection sequence for use with the disclosed system.