### 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
const std::string& event,
    content::NavigationHandle* navigation_handle) {
  bool is_main_frame = navigation_handle->IsInMainFrame();
  int frame_tree_node_id = navigation_handle->GetFrameTreeNodeId();
  content::FrameTreeNode* frame_tree_node =
      content::FrameTreeNode::GloballyFindByID(frame_tree_node_id);
  content::RenderFrameHostManager* render_manager =
      frame_tree_node->render_manager();
  content::RenderFrameHost* frame_host = nullptr;
  if (render_manager) {
    frame_host = render_manager->speculative_frame_host();
    if (!frame_host)
      frame_host = render_manager->current_frame_host();
  }
  int frame_process_id = -1, frame_routing_id = -1;
  if (frame_host) {
    frame_process_id = frame_host->GetProcess()->GetID();
    frame_routing_id = frame_host->GetRoutingID();
  }
  bool is_same_document = navigation_handle->IsSameDocument();
  auto url = navigation_handle->GetURL();
  return Emit(event, url, is_same_document, is_main_frame, frame_process_id,
              frame_routing_id);
}
void WebContents::Message(bool internal,