>>1917473it's an extremely rust resistant coating, literally won't rust from normal use. aesthetically it's a titanium-ish grey which some people might think is boring or won't match the rest of their bike but it goes well with certain parts like wheels mfg bottom brackets or the grey parts on certain SPD pedals. they might be hard to find at a good price outside of europe, especially the newer e-series chains.
if you check the reviews with google translate, a couple of them mention rust/corrosion:
https://www.rosebikes.com/kmc-e9-e-ept-derailleur-chain-9-speed-e-bike-2666252the singlespeed/internal gear hub versions in particular are incredibly long lasting
https://www.rosebikes.com/kmc-e1-ept-single-speed-e-bike-chain-for-gear-hubs-2677501 