It's oddly difficult to get information about the chain gang system that existed in the South until the 1950s and 60s. There are a few famous exposes, plus the pop culture images of "I Am a Fugitive from a Chain Gang," or "The Defiant Ones," or "Cool Hand Luke." There are an awful lot of white faces in these movies.
I was in our back yard in Tennessee sometime in the mid-50s when I saw a work gang in leg irons working on Emory Drive across the vacant lot that abutted our back yard. There were no white faces in that crowd.
The convict labor system was the way that southern states kept their roads repaired for most of the first half of the 20th Century. I've seen claims that the chain gangs were integrated, despite a fully segregated prison system, but I'm bound to wonder how much of that integrated chain gang image came from ignorance and poetic license. There was no mystery about how the prison labor system worked: whenever a road contractor needed labor, the local constabulary rounded up all the "vagrants" in the area, and vagrants were almost invariably black. Putting a white man in a largely black work gang would have been considered appalling.
Perhaps the gangs that were made up of prison inmates, rather than local "pick up" labor were different, but again, how and why would there be a mixing of populations that were not even in the same prisons? The logistics alone make the idea dubious; it would have been a lot like "forced busing," wouldn't it?
As for the pop culture images, there's no question about the dynamic at work there. There would have been no audiences for a film that featured only black characters, whereas adding black men to the mix either allows a statement about racial issues, or it emphasizes the degradation of the main (white) character.
In any case, I've just spent some time on Google Images, looking for a photo of a real chain gang with both black and white men in it, and I couldn't find any. I never saw one in real life, either.
The movie, "I Am a Fugitive from a Chain Gang," was based on a book, I Am a Fugitive from a Georgia Chain Gang. The State of Georgia banned the movie. I don't think they did it because it showed chain gangs; I think they banned it because it showed one that was integrated.