her hair??

In former years it was considered extremely scandelous for a woman to "do something" to her hair, i.e. color it somehow. It was identified with prostitution or some other kind of immorality. Recall the scene in Gone with the Wind (I believe in the book only) where Scarlett is noting that Rhett Butler's lady friend who runs the brothel (can't remember her name) is the first woman she's met who has "done something to her hair." Thus a well to do, respectable woman like Kate would never have admitted to coloring her hair, and would have been offended if someone insinuated it. However, she obviously did color her hair (after all, she is a woman wanting to be fashionable) and her husband and Jake think this is a great joke on her and her snobby self-righteousness. They obviously don't care if she has colored her hair (as I've noticed a lot of men really don't care about many of the things women do to try to be attractive) but they are enjoying turning the tables on her after she has gone on so much about the vulgarity and such of the town and people of McLintock.