Back color for MDI in C#.net

MdiClient ctlMDI;
            foreach (Control ctl in this.Controls)
            {
                try
                {
                   ctlMDI = (MdiClient)ctl;
                    ctlMDI.BackColor = Color.Yellow;
                }
                catch (InvalidCastException exc)
                {
                    MessageBox.Show(exc.Message);
                }
            }
            }