Some makers didn’t switch, some used both. The S.D. Myres holster I ordered in 1968 or 9 has a brass snap, I know I ordered a brass buckle on the matching belt.
During WW II Heiser used a base metal snap for a while as brass was needed by the US forces.
Myres holsters from the same time period may have either type,Lawrence used primarily nickel snaps.
Maybe Red will enlighten us.
Regards,
The material in snaps is a bigger topic than it appears. Since about 1940 gunleather makers have used what's called a Dot snap fastener and it has been made in all-brass material, in all steel, in all stainless steel. Then all those materials have been plated, too, in brass, nickel, black oxide, enamel, etc. Then all these pieces are mixed by the gunleather maker, too!
Steel parts, of course, will rust. Brass I think was used originally because of saltwater exposure; it's the one that creates verdigris (the green stuff) when in contact with veg leather esp. brown oiled leather. Stainless then is ideal for all uses.
There was a period circa 1970s when Perkins at Safariland was successful in persuading agencies that the mere appearance of hardware made uniformed officers look like soldiers; so he made good money either covering the cap of the snap or substituting velcro that itself was brand new in the 1960s. Many of us, including at Bianchi, made the switch to the nylon covers built into the cap of these same metal snaps.
The query is likely about the color of the cap, which was strictly an ornamental decision. The Army used brass on its hardware including the Sam Browne buckles, and the snaps expected to match; the belts were typically brown horsehide. The Sam Browne was adopted for WWI and that leaked over into law enforcement; in their case black was settled on and nickle hardware for them became the standard. The likes of CHP in the '60s onwards wanted brass as I recall. There were even black plated metal buckles. Sheriffs departments around USA often wanted brown leather and brass hardware, usually basketweave.
I have tens of thousands of gunleather images and see that none of them have brass snaps! I fully expected to find what I wanted in my Tex Shoemaker subfolder because Sheriff's departments were his cup of tea. This is one of his in floral carved; when the snap is against the body then these were not necessarily expected to match the buckle: