When running a Qt application on the Gnome desktop, with the gtk3 platform theme, the palette colors that are read from QGtk3Storage::palette(SystemPalette) are light when high contrast is enabled on the system, even when using a dark system appearance.

There's a chance that this is intentional behavior or a bug in gtk3, but further investigation is needed. The assumed intended behavior is in my opinion that the palette colors returned from that function should reflect the associated color scheme. Currently you get a white'ish background and dark'ish windowText color even when using a dark system theme, as long as high contrast mode is enabled on the system.