Fading it is also unnecessary in most applications. Gnome apps need to do it because they have no titlebar, but this isn't a problem in most cases, and xfwm can draw titlebars just fine.
I know I can manually overload the GTK theme's backdrop properties but I was kind of hoping someone on the Interwebs found a way that doesn't require me to drag .css hacks over umpteen computers.
Background: a good chunk of my work involves things like comparing simulation and measurement results among multiple applications/windows. Text in inactive windows being unreadable is a little counterproductive when I try to do that. I begrudgingly put up with the huge widgets but having to squint at screens for eight hours a day is not fun.
(FWIW, Adwaita is even worse).