I bought this ZHF reservoir over winter and it doesn't show on the cap what fluid, however, I know its ATF since it says so on my stock cap.
You could swap caps on the new reservoir to keep the indication of fluid present, or maybe mark with white out somewhere on the reservoir "ATF" to help future owners.
Personally I just swapped reservoirs and refilled with fresh ATF as I'm well aware mine wasn't taking CH-11ES.