radDock Color

Hello,

When setting the property this.IsMdiContainer = true;
the main form changes color, how can I change the color?

       private void MenuPrincipal_Load (object sender, EventArgs e)
         {
            this.IsMdiContainer = true;
            this.radDock1.AutoDetectMdiChildren = true;
         }
        private void radButton1_Click (object sender, EventArgs e)
         {
             radForm1 form = new radForm1 ();
             form.Text = "Test Form" + DateTime.Now.ToShortTimeString ();
             form.MdiParent = this;
             form.Show ();

         }

Here I show the photo

Thank you.