Try this:

Code:
Private Const WS_EX_TRANSPARENT = &H20&
Private Const GWL_EXSTYLE = (-20)

Private Declare Function SetWindowLong Lib "user32" _
  Alias "SetWindowLongA" (ByVal hwnd As Long, _
  ByVal nIndex As Long, ByVal dwNewLong As Long) As Long


Private Function MakeListTransparent(ListCtl As Object) As Boolean

    On Error Resume Next
    ListCtl.BackColor = ListCtl.Parent.BackColor
    SetWindowLong ListCtl.hwnd, GWL_EXSTYLE, WS_EX_TRANSPARENT
    MakeListTransparent = Err.LastDllError = 0

End Function


Usage


MakeListTransparent List1