function GetWindowQTColor() : TColor;
var
PaletteH : QPaletteH;
ABrush : QBrushH;
APQColor : PQColor;
begin
PaletteH := QPalette_Create; // https://doc.qt.io/qt-5/qpalette.html
QGuiApplication_palette(PaletteH); // https://doc.qt.io/qt-5/qguiapplication.html
ABrush := QPalette_Window(PaletteH);
APQColor := QBrush_color(ABrush);
Result := RGBtoColor(APQColor^.r div 256, APQColor^.g div 256, APQColor^.b div 256);
// PaletteH.free; // NO, don't do this.
QPalette_destroy(PaletteH); // zeljko says (below) do this and it works !
end;