Everyone in the movie is black. As far as I know, almost everyone who worked on it was black. It was made for black audiences. As an aside, the illegitimacy rate for blacks at the time was about 15%. It's a wildly different world and if you watch it, you need to get out of a 2017 mindset and try to immerse yourself in the culture of the past. The movie could never be made today for a variety of reasons, all cultural.
The movie is really a series of performances by about 8 of the biggest colored musical, dance and comedy acts of the era, tied together with a very thin story line. I enjoyed what little acting the cast got to do. The whole thing was delightful.
As I watched it, I tried to put my finger on just what it was. I finally figured out an analogy. These days, one can go to a music festival and see a bunch of bands in succession. Stormy Weather is a celluloid version of a music festival. It's Coachella in 1943. Lena Horne is the headliner with Fats and Cab Calloway providing a couple of numbers as well. Other acts get one performance each and all save the Cake Dance are terrific. The Cake Dance was simply alien, part of a bygone era that I couldn't comprehend.
Below is one of the performances that blew me away. I'm sure it blew away the white musicians of the time as well. I could see Louis Prima and Harry James being deeply influenced by the artistry of the performers. I can't tell if I prefer Fred Astaire and Gene Kelly over the dancers in the movie. I think Astaire and Kelly give better routines, but is that because they had more money for more takes? Who knows. In any case, enjoy. And take some time to watch it if you get a chance. It's available on Amazon video.