Flutter – How to set the appBar color to be REALLY White?

I want my app bar to be really White, still using the material 3 design.
I’ve tried to use
backGroundColor: Colors.white
either in the ThemeData of the app or directly in the widget. Nothing changes.

Here my code:

  static ThemeData lightTheme = ThemeData(
    useMaterial3: true,
    brightness: Brightness.light,
    primaryColor: Colors.white,
    appBarTheme: const AppBarTheme(
      backgroundColor: Colors.white,
    ),
  );
}

return Scaffold(
       appBar: AppBar(
           elevation: 20,
           backgroundColor: Colors.white,
           title: Widget()
       )
      )

I don’t want that Grey color. I just want the White.

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