C++ Windows API изменить Background окна

case WM_ERASEBKGND: {
  HPEN pen;
  HBRUSH    brush;
  RECT rect;
  pen = CreatePen(PS_SOLID, 1, this->background);
  brush = CreateSolidBrush(this->background);
  SelectObject((HDC)wParam, pen);
  SelectObject((HDC)wParam, brush);
  GetClientRect(hwnd, &rect);
  Rectangle((HDC)wParam, rect.left, rect.top, rect.right, rect.bottom);
  break;
}    
case WM_PAINT: {
  hdc = BeginPaint(hwnd, &ps);
  // TODO: Add any drawing code here...
  EndPaint(hwnd, &ps);
  break;
}

и

bool Window::SetBackground(COLORREF background) {
  this->background = background;
  InvalidateRect(this->hwnd, NULL, TRUE);
  return true;
}

Почему вызов метода (после создания окна) не изменяет Background окна?