* Electron version: 1.7.5

### Expected behavior

When a theme color is no longer present the webContents did-change-theme-color event should return `null`.

### Actual behavior

The event returns `"#000000"`.

### How to reproduce

1. Log the returned color of the webContents did-change-theme-color event.
2. Go to https://electron.atom.io which has a theme color.
3. Go to https://atom.io which does not have a theme color.




atom/browser/api/atom_api_web_contents.cc
const content::SavePageType& save_type,
                           const SavePageHandler::SavePageCallback& callback) {
  auto handler = new SavePageHandler(web_contents(), callback);
  return handler->Handle(full_file_path, save_type);
}
void WebContents::OpenDevTools(mate::Arguments* args) {
  if (type_ == REMOTE)
    return;
  if (!enable_devtools_)
    return;
  std::string state;
  if (type_ == WEB_VIEW || !owner_window()) {
    state = "detach";
  } else if (args && args->Length() == 1) {
    bool detach = false;
    mate::Dictionary options;
    if (args->GetNext(&options)) {
      options.Get("mode", &state);
      
      options.Get("detach", &detach);
      if (state.empty() && detach)
        state = "detach";
    }
  }
  managed_web_contents()->SetDockState(state);
  managed_web_contents()->ShowDevTools();
}
void WebContents::CloseDevTools() {