QWebEnginePage.setBackground(Qt::black) doesn't work for page loading.

I am working on a local application that is mostly dark. When we load different pages, there is always a white flash during page loading.

We tried to use QWebEngineView -> page().setBackground(Qt::black), but the only thing that changes is the initial background and nothing more.

The related doc  https://doc.qt.io/qt-6/qwebenginepage.html#backgroundColor-prop is not describing the reality:

>> you can set it to match your web content in a hybrid application to prevent the white flashes that may appear during loading.

But it cannot.

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Minimal codes sample:

Two black web pages and a button to load between them. Click and you will see the white flash during loading.

https://github.com/SourceReviver/qtwebengine_bg_not_work