When I was reviewing a lot of C&O box car photos, I got the impression that in the Progress-logo era (starting 1948) many repaints didn't get black ends. Yet new "red" / "brown" cars were continuing to come, at least from Pullman-Standard, with black ends for many years.
Usually I couldn't see enough to judge about the roofs or underbodies. For my models, I went with all-one-color.
But I do recall a funky older-than-1937-design box car-- which shows up on a video which includes a bit of rare steam action in color from the mid-1950s-- which clearly had black ends.

Scott Pitzer