Steel chain comes in several finishes. The shiny hardware store chain has a zinc plating to keep it from rusting. Zinc oxidizes with the acid in you perspiration and leaves a black or dark gray stain if worn for longer than a few hours. The stain washes off skin easily enough but is difficult to get out of clothes. Still, zinc chain is cheap and readily available and is widely used for bondage.
Chains designed for water use (boat anchor chains for instance) have a hot dipped galvanized coating which a dull silver or gray coating. Galvanized coating is another form of zinc coating and will stain as described above. Galvanized coating is generally rougher than the shiny zinc plating or plain steel and the chain is more expensive. However, if you plan to chain your Andromeda to the rocky sea shore and the kraken might take a couple years to show up, galvanized will do the job. Lucky Andromeda!
Heavier chains can be bought with no finish at all, just the steel itself. In time, these chains will rust. If you are building an old school damp dungeon, rusty chains might be just the thing.
Most chain is available in stainless steel which is pretty much the gold standard for bondage. It doesn’t corrode and looks great. Stainless is slightly stronger than Grade 30 steel (1,570 lbs working load vs 1,300 lbs for 1/4” chain). Stainless is also expensive but if you want an unobtrusive permanent collar, wrap a length of 3/16” stainless twist chain around your neck and lock it in place.
I’ve also seen some heavier proof coil chain with what looks like a cadmium coating. It’s a yellow-gold plating. Cadmium plating does a good job of preventing rust on nuts and bolts but I haven’t used any of the chain for bondage yet.