I'm a little puzzled as you're describing a music stylist on skin colour, black vs white. I presume you don't really mean that, so what distinguishes the two musical styles, black swing vs white swing? Serious question.
For me (and I don't judge people for thinking differently) there's a certain joie de vivre in the music that is just lacking from what white musicians released commercially. I know they were capable of it (I once found a recording of Glenn Miller swinging it just as hard as anything Basie put out) but they were playing to their audience at the time. As I've learned more about the history of Swing and Lindy Hop, this was a specific choice made to "civilize" (as the white people of the time would have said) Jazz's savage rhythms. There's actually posters from the Arthur Murray school in the 1940s saying this exact thing.
(Aside, I had a friend who played a radio show in the 2000s playing old Jazz music. She told me once that if she put anything from a black musician on the show, she'd get hate mail from the listeners. Go figure.)
You may not realize this, but in the 1930-1950 era being described in America, there was something called "Segregation" where black people were considered legally inferior to white people. As such, there was a very hard line between "black" and "white", a line that was aggressively enforced by every level of society from lawmaking, policing and justice, to radio and TV access, to education, to neighborhoods, and frankly everything else.
With that context, I think it's very easy to see how there can be "black swing" and "white swing" -- it was in a society that forcibly separated everything into "black X" and "white X".
And then Coltrane and Orman and Davis come and change the whole jazz world.
My point is if the music actually is so different, it should be noticable and describable without knowing the race of a particular artist. So how would you describe the black music that describes only black musicians but not white musicians from this period, and vice versa.
The most obvious difference is the energy level and "rawness" of songs - those white bands had really carefully choreographed performances with minimal deviation, even solos were often written out in similar big bands.
Black musicians often shouted, yelled or mugged during performances - all of these are completely absent in white performances at that time.
The brain can categorize much more easily than it can create a concrete definition for those categories.
For some reason, the view is widely held that internal thoughts are expressed in words. This would mean that anything you can think can easily be verbalized.
The fact that this view is quite obviously false seems to bother very few people.
Talking about the arts is difficult. In everyday conversation, well known phrases for describing the arts include “I know it when I see it” and “if you have to ask, then you’ll never know”. I’m a fan of “writing about music is like dancing about architecture”. It just isn’t easy to describing differences in performance and interpretation.
Since it’s widely recognised that describing music is difficult, and since you’re familiar with the artists in question, perhaps you could accept the point in good faith or put into words why you don’t think they are any different?
They are and I can, however the existence of Black Swing is in no way predicated on a difference in sound only.
Consider this: white culture in America continually stole from a legally repressed black culture, including white swing which stole the black art and commercialized it. Even if a 1950 white swing song sounds similar to a 1940 black swing song, there is still a "black swing" and a "white swing".
Frankly, I think trying to reduce history of music down to "the sounds themselves" is a way to whitewash the history and destroy the true knowledge of what happened and why. The context is very important.
Like how the Blues didn't come out of a comfortable lifestyle.
Looking of that period is a very sobering reminder of a very dark stain in our national history - and I’ve read too many stories about even well known performers being told they can’t play at certain venues or have to leave immediately afterwards to think everyone wasn’t aware of the stakes:
https://en.wikipedia.org/wiki/Mass_racial_violence_in_the_Un...
As an example of how widespread this was, it took Marilyn Monroe at the height of her fame intervening for _Ella Fitzgerald_ to be able to play at a club in Los Angeles! Not the Deep South, not 1917, but very modern California.
> In October 1957 Monroe made a call to the Mocambo nightclub in Los Angeles, on behalf of Fitzgerald. Monroe used her social status and popularity to make a deal with them. If they allowed Fitzgerald to perform, Monroe promised that she would take a front-row seat every night
https://americanhistory.si.edu/explore/stories/ella-fitzgera...
The closest I can come to a silver lining for this is that it allowed more artists to find a niche where they weren’t competing with the major national artists but that’s nowhere close to compensation for so much tragedy.