Yes, 1957. I believe the RS-11s delivered that year were the first engines to wear the simplified scheme (though with a "script" herald slightly different than the one adopted a bit later).
Like this Atlas N scale model:
https://www.walthers.com/alco-rs11-standard-dc-master-r-new-york-central-8003-black-white
November, 1957.
Good Luck, Ed
When did New York Central switch from the lightning stripe paint scheme to the cigar band scheme?