Winchester No.10 Nublack

I read in the “old” forum that "Another load that you might run across is a 6 inch 10 Gauge in both salmon colored paper with brass head with the headstamp “WINCHESTER No 10 NUBLACK MADE IN U.S.A.” or an all aluminum case with no headstamp… These are smoke marker shells for use in a 25 pound practice bomb. The official designation is "10 GA PRACTICE BOMB SIGNAL, AN-Mk-4. They give off a large plume of white smoke to show the pilot where the bomb landed."
Now, this shotshell is beige. Does the word “Nublack” convey any particular meaning (like bomb signal) or it is just a brand?

Vlad–Nublack was a Winchester brand name for a shotshell line made in the 1930’s. The 6" round you picture was the predecessor of the aluminum one you described and were used in the same 25 practice bombs. They were also used in a 5 lb practice bomb. The 25 lb. bombs were blue and tear-drop shaped while the 5 lb. were orange and cylindrical with a big flat striker plate at the front. The 25 lb. had the drop characteristic of a General Purpose Demolition Bomb, The 5 lb simulated a certain type of nuclear bomb.

Thanks, Ron, but my shell is 2.5 inches, not 6.

The Nublack headstamp was used since 1905 (trademark filled April 27). Here is a description of the factory load in yellow (1914):

The NUBLACK was offerred until about 1938, so it had a long run into the smokeless era.