Abstract: An ink cartridge for an inkjet printer includes a housing for supporting an ink supply in a cavity within the cartridge housing and a color or ink type discrimination structure connected to the cartridge housing, the color discrimination structure being when assembled a generally cylindrical structure having a keyway formed therein wherein the color or ink type discrimination structure may be oriented through rotation about the central axis of the cylindrical structure in one of plural allowable orientations when the cartridge housing is assembled or after assembly to define a color or ink type of ink in the cartridge. Thus, the same structure or parts may be used in different cartridges containing ink of different colors but yet provide color discrimination.