procedure TForm1.ToolBar1AdvancedCustomDraw(Sender: TToolBar;
  const ARect: TRect; Stage: TCustomDrawStage; var DefaultDraw: Boolean);
begin
  if Stage = cdPrePaint then
  begin
    Sender.Canvas.Brush.Color := Sender.Color;
    Sender.Canvas.FillRect(ARect);
    // keep the DefaultDraw on True
  end;
end;