MDI forms, accessing controls

Question

One form has a checkbox. How do I access the state of this checkbox in the code of another form class (or any other control)? I tried changing private to public in the designer. When I set the main form to this.IsMDiContainer = true in the designer, it makes the entire background color of the form nasty gray but the controls keep their color. Any idea how to stop this. Also, how do I get the child form to not let the parents controls show through.