如何禁止一个控件而不变灰？

procedure EnableControl(AControl: TWinControl; Enable: Boolean);
begin
  with AControl do
    if Enable then
      SetWindowLong(Handle, GWL_STYLE, (not WS_DISABLED) and
        GetWindowLong(Handle, GWL_STYLE))
    else
      SetWindowLong(Handle, GWL_STYLE, WS_DISABLED + GetWindowLong(Handle,
        GWL_STYLE));
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  EnableControl(BitBtn1, False);
  BitBtn1.Font.Color := clGreen;
end;