### Preflight Checklist

- [X] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/main/CONTRIBUTING.md) for this project.
- [X] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/main/CODE_OF_CONDUCT.md) that this project adheres to.
- [X] I have searched the [issue tracker](https://www.github.com/electron/electron/issues) for a feature request that matches the one I want to file, without success.

### Electron Version

14.0.1

### What operating system are you using?

macOS

### Operating System Version

macOS Big Sur 11.6.1

### What arch are you using?

x64

### Last Known Working Electron version

14.0.0

### Expected Behavior


When `BrowserView.setBackgroundColor` is called with an explicit color, expect the background to be the color selected.

When `BrowserView.setBackgroundColor` is not called, expect the background of the `BrowserView` to be transparent by default; and can see through `BrowserWindow`'s background color.



### Actual Behavior

The `BrowserView` background is always white.

### Testcase Gist URL

https://gist.github.com/kevinlinv/2de60478ffec6a2f18f1ec0fc6f5add9

### Additional Information

Here is a quick recording that reproduces the error.

https://user-images.githubusercontent.com/44967897/140694174-e27aff28-1847-4813-bc46-d9fda6569128.mp4


shell/browser/api/electron_api_web_contents.cc
auto handle = FromOrCreate(
      isolate, inspectable_ontents_->GetDevToolsWebContents());
  devtools_ontents_.Reset(isolate, handle.ToV8());
   Set inspected tabID.
  base::Value tab_id(ID());
  inspectable_ontents_->CallClientFunction("DevToolsAPI.setInspectedTabId",
                                                &tab_id, nullptr, nullptr);
   Inherit owner window in devtools when it doesn't have one.
  auto* devtools = inspectable_ontents_->GetDevToolsWebContents();
  bool has_window = devtools->GetUserData(NativeWindowRelay::UserDataKey());
  if (owner_window() && !has_window)
    handle->SetOwnerWindow(devtools, owner_window());
  Emit("devtools-opened");
}
void WebContents::DevToolsClosed() {
  v8::Isolate* isolate = JavascriptEnvironment::GetIsolate();
  v8::Locker locker(isolate);
  v8::HandleScope handle_scope(isolate);
  devtools_ontents_.Reset();
  Emit("devtools-closed");
}
void WebContents::DevToolsResized() {
  for (ExtendedWebContentsObserver& observer : observers_)
    observer.OnDevToolsResized();
}
void WebContents::SetOwnerWindow(NativeWindow* owner_window) {
  SetOwnerWindow(GetWebContents(), owner_window);
}
void WebContents::SetOwnerWindow(content::WebContents* ontents,
                                 NativeWindow* owner_window) {