Black paint .L.O.L. Is it removable, if so you can have it black oxide treated. They can do it on stainless. Roger C.
Have a commercial outfit do it . It is a hot application and you don't want it to come out $hity. Roger C.
A couple of options-- one just mask it and use a spray primer and then use a spray stove black--- that will be durable or if you just want it duller--- just mask the barrel and sandblast or bead blast the top
My wife had some flat black craft paint that I put on it. When I went to sell the gun I just wiped it right off with some Goof-Off.