The default behavior is to make the client container use the Control color from the Control panel. You can change this behavior by making the MDI Client container use the form's BackColor and Image. To do this, after the call to InitializeComponents(), add the code below. You can also download a working MDI Client project that has this code in it.

//set back color 
foreach ( Control c in Controls ) 
{ 
  if ( c is MdiClient ) 
  { 
    c.BackColor = BackColor; 
    c.BackgroundImage = BackgroundImage; 
  } 
}

Contributed from George Shepherd's Windows Forms FAQ