Describe the bug

Setting WebView2.DefaultBackgroundColor to transparent results in a Background that seems to be equivalent to the color of ApplicationPageBackgroundThemeBrush (e.g. 32, 32, 32 in Dark theme). That is not what I want. And changing the RequestedTheme at runtime after CoreWebView2 has initialized has no effect on the background color. Moreover, changing the RequestedTheme has no effect at all, the WebView2 control seems to set the background based on the ApplicationTheme which cannot be changed at runtime.

Steps to reproduce the bug

XAML:

<Grid Background="Red">
  <WebView2 DefaultBackgroundColor="Transparent" Loading="WebView2loading"></WebView2>
</Grid>

C#:

private async void WebView2loading(FrameworkElement sender, object args)
{
  await ((WebView2)sender).EnsureCoreWebView2Async();
}

Expected behavior

The expected behavior is that setting the BackgroundColor to transparent should set the background color to transparent.

Screenshots

The Background should be red in the example.

NuGet package version

WinUI 3 - Windows App SDK 1.0 (If you're seeing your issue in older previews of WinUI 3, please try this release)

Windows app type

• UWP
• Win32

Device form factor

Desktop

Windows version

Insider Build (xxxxx)

Additional context

Testet on 21H2 (22000.376)