I can't see what you're alluding to in the quote from "A Time to Kill". It's been a few years since I last read that book but my memory of it is that he was sympathetic toward Carl Lee. Leathery sold can describe the feet of anyone who customarily goes barefoot when outdoors, as I did when I was in college and unwilling to waste what little money I had on shoes. I had very thick calluses on my feet and I could walk on hot pavement or gravel without much difficulty. I certainly had leathery soles. My feet weren't black although after a walk outside it might be hard to tell that.
I think you're mistaking what Grisham did in that book.
I decided before I hit Post I'd better check the book and make sure I was right. Well, I'm basically right and you're way off. I did searches and the word "padding" doesn't appear in the book. The only reference to barefoot refers to Lucien Wilbanks, an elderly lawyer who helps the defense.
"Leathery" does appear, describing the feet of Leroy, Carl Lee's cellmate.
I think you got this one wrong.
Barry