Supply items, such as toner bottles for laser printers, include substantially identical housings amongst the many different colors of toners. To distinguish the items and prevent improper installation, a keying structure attaches per each bottle and is indexed relative to adjacent items. In one aspect, indexing includes rotating a knob of the keying structure about a central axis to provide different keying orientations to an imaging unit in the printer. During installation, users mate the knob with variously arranged channels in a wall defining a slot for receiving the bottles. A lengthy flange on the bottle mates with a lengthy slit of the wall to provide installation stability. Other embodiments contemplate delaying engagement of a shutter on the bottle that prevents the toner from communicating with the imaging unit until the mating of the keying structure is assuredly made relatively proper. This prevents inadvertent mixing of toner colors.