' Create a new form.
Dim mdiChildForm As New Form

Private Sub Form1_Load(ByVal sender As Object, _
    ByVal e As System.EventArgs) Handles MyBase.Load

    ' Set the IsMdiContainer property to true.
    IsMdiContainer = True

    ' Set the child form's MdiParent property to 
    ' the current form.
    mdiChildForm.MdiParent = Me

    'Call the method that changes the background color.
    SetBackGroundColorOfMDIForm()
End Sub

Private Sub SetBackGroundColorOfMDIForm()
    Dim ctl As Control

    ' Loop through controls,  
    ' looking for controls of MdiClient type. 
    For Each ctl In Me.Controls
        If TypeOf (ctl) Is MdiClient Then

            ' If the control is the correct type,
            ' change the color.
            ctl.BackColor = System.Drawing.Color.PaleGreen
        End If
    Next

End Sub

// Create a new form.
Form mdiChildForm = new Form();

private void Form1_Load(object sender, System.EventArgs e)
{

    // Set the IsMdiContainer property to true.
    IsMdiContainer = true;

    // Set the child form's MdiParent property to 
    // the current form.
    mdiChildForm.MdiParent = this;

    // Call the method that changes the background color.
    SetBackGroundColorOfMDIForm();
}

private void SetBackGroundColorOfMDIForm()
{
    foreach ( Control ctl in this.Controls )
    {
        if ((ctl) is MdiClient)

            // If the control is the correct type,
            // change the color.
        {
            ctl.BackColor = System.Drawing.Color.PaleGreen;
        }
    }

}

// Create a new form.
private Form mdiChildForm = new Form();

private void Form1_Load(Object sender, System.EventArgs e)
{
    // Set the IsMdiContainer property to true.
    set_IsMdiContainer(true);

    // Set the child form's MdiParent property to 
    // the current form.
    mdiChildForm.set_MdiParent(this);

    // Call the method that changes the background color.
    SetBackGroundColorOfMDIForm();
} //Form1_Load

private void SetBackGroundColorOfMDIForm()
{
    for (int iCtr = 0; iCtr < this.get_Controls().get_Count(); iCtr++) {
        Control ctl = this.get_Controls().get_Item(iCtr);
        if (ctl instanceof MdiClient) {
            // If the control is the correct type,
            // change the color.
            ctl.set_BackColor(System.Drawing.Color.get_PaleGreen());
        }
    }
} //SetBackGroundColorOfMDIForm