Private client As New MdiClient
 
    Public Sub New()
 
        ' This call is required by the Windows Form Designer.
        InitializeComponent()
 
        For Each c As Control In Me.Controls
            If TypeOf c Is MdiClient Then
                client = c
                client.BackColor = Color.Red
                Exit For
            End If
        Next c
    End Sub

mfG.
Stephan