There has been some discussion on the kde-core-devel mailing list about a change to how the active window should be distinguished from the inactive windows, where different color palettes are used for the widgets inside inactive windows.
I tried out the change yesterday, testing flipping between Konsole and Dolphin, and don't personally like it much. Here are a couple of screen shots of what I saw so you can judge for yourself (with a KDE3 kicker in there):
Konsole at front with Dolphin
Konsole with Dolphin at front