Why do the film makers have Bob Ewell and Tom Robinson in the same costumes

This is interesting. I think Bob Ewell tries hard to portray himself as superior to Tom Robinson simply because he is white, and Tom is black. The director has them wear similar clothes to juxtapose the two: to show just how weak, dirty and pathetic Bob is compared to Tom. While Tom is a muscular proud and clean-cut respectful Negro gentleman, Bob is a small weasel-like racist who wears similar clothes but is filthy and repellent.