TWinControl.DefaultHandler处理WM_CTLCOLORMSGBOX..WM_CTLCOLORSTATIC消息的两个参数很有意思，两个都是传递句柄

procedure TWinControl.DefaultHandler(var Message);
begin
  if FHandle <> 0 then
  begin
    with TMessage(Message) do
    begin
      if (Msg = WM_CONTEXTMENU) and (Parent <> nil) then
      begin
        Result := Parent.Perform(Msg, WParam, LParam);
        if Result <> 0 then Exit;
      end;
      case Msg of
        WM_CTLCOLORMSGBOX..WM_CTLCOLORSTATIC:
          Result := SendMessage(LParam, CN_BASE + Msg, WParam, LParam); // 它的LParam是一个句柄，它的WParm是一个HDC（可以看SetBkColor的MSDN说明），消息本身只被用来做转换，然后被丢弃
        CN_CTLCOLORMSGBOX..CN_CTLCOLORSTATIC:
          begin
            SetTextColor(WParam, ColorToRGB(FFont.Color));
            SetBkColor(WParam, ColorToRGB(FBrush.Color));
            Result := FBrush.Handle;
          end;
      else
        if Msg = RM_GetObjectInstance then
          Result := Integer(Self)
        else
        begin
          if Msg <> WM_PAINT then
          Result := CallWindowProc(FDefWndProc, FHandle, Msg, WParam, LParam);
        end;
      end;
      if Msg = WM_SETTEXT then
        SendDockNotification(Msg, WParam, LParam);
    end;
  end
  else
    inherited DefaultHandler(Message);
end;

但是我搞不明白WM_CTLCOLORMSGBOX本身是不是标准Windows消息呢？好像是，但是不能在MSDN中直接查到，只能从许多VC的文章里间接的见到。

https://msdn.microsoft.com/fr-fr/library/cc485255(v=vs.71).aspx

但是WM_CTLCOLORSTATIC是Windows标准消息：
https://msdn.microsoft.com/fr-fr/library/windows/desktop/bb787524(v=vs.85).aspx

这里写的清清楚楚，两个参数的作用：
wParam : Handle to the device context for the static control window.
lParam : Handle to the static control.