What makes it for me is that the ivory or cream colored trousers are wool, from what I can see. When people wear a light colored trouser, it's usually white cotton khaki or white denim. The ivory trousers in wool gabardine or flannel drape better and look elegant, even glamorous in a 1920s way.
Thanks, all. For those who asked, RLPL jacket and RLPL cream wool trousers.