single main menu control usage in multiple forms

Question

problem:
I created a fomr (Form1) ,and in it created a MainMenu Object(mainMenu1) having menuItem1 (Red)),and tried as fallows

private void menuItem1_click(----)
{
      this.BackColor=Color.red;
}
private void button1_click(System.Object sender,System.EventArgs e)
{
        Form obj=new Form();
        obj.Mebu=mainMenu1;
        obj.show();
}
Now if i click button1 in form1 and use the menuItem1 the Form1 color is changing
How to chang color of Form object

waiting for reply.
 thanking you.
Karra.Parameshwar Reddy