The drawing code for CC_TitleBar is unnecessary complex wrt the painting of the icons. It seems the idea was to use some kind of alpha blending for the painting but it was never implemented and the two colors have the same value since 2012:

QColor textColor(active ? 0xffffff : 0xff000000);
QColor textAlphaColor(active ? 0xffffff : 0xff000000 );

Therefore the code should be cleaned up.

Repoducer code:

QMdiArea area;
auto sub = new QMdiSubWindow;
sub->setWindowIcon(sub->style()->standardIcon(QStyle::SP_MediaVolumeMuted));
area.addSubWindow(sub);
auto sub2 = new QMdiSubWindow;
area.addSubWindow(sub2);
sub->showNormal();
sub2->showNormal();
area.resize(100, 100);
area.show();