For some reason my KDE does not have Colors:View/BackgroundNormal setting present, and all the KDE apps are working correctly. But fusion and and plastique became absolutely unusable at once. Took me couple of hours to debug into QKdeThemePrivate::readKdeSystemPalette to see that I'm missing one single property, and that property is defaulted to black instead of white, so all the views and context menus have black background for black font.

Fix is obvious - to add that property to kdeglobals file, but it looks like KDE defaults that color to white, meaning that Qt should too.