Add spec for CoreWebView2ControllerOptions.DefaultBackgroundColor.md for review

specs/CoreWebView2ControllerOptions.DefaultBackgroundColor.md

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+CoreWebView2ControllerOptions.DefaultBackgroundColor
+===
+# Background
+
+Previously, there was a fix to address an issue where the background color controller property
+was applied too late, causing a disruptive white flash during the WebView2 loading process.
+
+This fix required using an environment variable. However, this workaround was not meant to be 
+a long-term solution. Therefore, we need to add this setting to `ICoreWebView2ControllerOptions` 
+to apply the color early in the loading process.
+
+# Description
+
+This interface extends the `ICoreWebView2ControllerOptions` to expose the `DefaultBackgroundColor` 
+property as an option.
+The `CoreWebView2ControllerOptions.DefaultBackgroundColor` API  allows users to set the 
+`DefaultBackgroundColor` property at initialization.
+
+This is useful when setting it using the existing [`CoreWebView2Controller.DefaultBackgroundColor API`](https://learn.microsoft.com/en-us/dotnet/api/microsoft.web.webview2.core.corewebview2controller.defaultbackgroundcolor?view=webview2-dotnet-1.0.2792.45)
+applies the color too late.
+
+
+
+# Examples
+
+## Win32 C++
+```cpp
+ HRESULT AppWindow::CreateControllerWithOptions()
+{
+    wil::com_ptr<ICoreWebView2ControllerOptions> options;
+    HRESULT hr = m_environment->CreateCoreWebView2ControllerOptions(&options);
+
+    if (hr == E_INVALIDARG)
+    {
+        ShowFailure(hr, L"Invalid profile name.");
+        return S_OK;
+    }
+
+    wil::com_ptr<ICoreWebView2ControllerOptions4> options4;
+    auto result = options->QueryInterface(IID_PPV_ARGS(&options4));
+
+    if (SUCCEEDED(result))
+    {
+        COREWEBVIEW2_COLOR wvColor{255, 85, 0, 225};
+        options4->put_DefaultBackgroundColor(wvColor);
+    }
+
+    m_environment->CreateCoreWebView2ControllerWithOptions(
+        m_mainWindow,
+        options.Get(),
+        Callback<ICoreWebView2CreateCoreWebView2ControllerCompletedHandler>(
+            this, &AppWindow::OnCreateCoreWebView2ControllerCompleted).Get());
+
+    return S_OK;
+
+}
+```
+
+
+
+## C#
+```c#
+public MainWindow()
+{
+    InitializeComponent();
+    SetDefaultBackgroundColor();
+}
+
+private async Task
+SetDefaultBackgroundColor()
+{
+    CoreWebView2Environment environment = await
+    CoreWebView2Environment.CreateAsync();
+    CoreWebView2ControllerOptions options = environment.CreateCoreWebView2ControllerOptions();
+    options.DefaultBackgroundColor = Color.FromArgb(255, 85, 0, 255);
+    await WebView2.EnsureCoreWebView2Async(environment, options);  
+}
+
+```
+
+
+
+# API Details
+
+## Win32 C++
+ ```cpp
+/// This interface extends the ICoreWebView2ControllerOptions interface to expose 
+/// DefaultBackgroundColor property. It is encouraged to transition away from the 
+/// environment variable and use this API solution to apply the property.
+
+[uuid(df9cb70b-8d87-5bca-ae4b-6f23285e8d94), object, pointer_default(unique)]
+interface ICoreWebView2ControllerOptions4 : ICoreWebView2ControllerOptions3 {
+
+  /// This API allows users to initialize the `DefaultBackgroundColor` early,
+  /// preventing a white flash that can occur while WebView2 is loading when
+  /// the background color is set to something other than white. With early
+  /// initialization, the color remains consistent from the start. After
+  /// initialization, `ICoreWebView2Controller2::get_DefaultBackgroundColor`
+  /// will return the value set using this API.
+  ///
+  /// The `DefaultBackgroundColor` is the color that renders underneath all web
+  /// content. This means WebView renders this color when there is no web 
+  /// content loaded. When no background color is defined in WebView2, it uses
+  /// the `DefaultBackgroundColor` property to render the background.
+  /// By default, this color is set to white.
+  ///
+  /// Currently, this API only supports opaque colors and full transparency. It will
+  /// fail for colors with alpha values that don't equal 0 or 255.
+  /// When WebView2 is set to be fully transparent, it does not render a background,
+  /// allowing the content from windows behind it to be visible.
+
+  [propget] HRESULT DefaultBackgroundColor([out, retval] COREWEBVIEW2_COLOR* value);
+  [propput] HRESULT DefaultBackgroundColor([in] COREWEBVIEW2_COLOR value);
+
+}
+```
+
+
+
+## .NET WinRT
+
+```cpp
+namespace Microsoft.Web.WebView2.Core
+{
+    runtimeclass CoreWebView2ControllerOptions
+    { 
+        // ...
+        [interface_name("ICoreWebView2ControllerOptions4")]
+        {
+             Windows.UI.Color DefaultBackgroundColor { get; set; };
+        }
+    }
+    }
+}
+
+```