C# WPF 핸들 사용하기

IntPtr mainWindowPtr = new WindowInteropHelper(this).Handle;

HwndSource mainWindowSrc = HwndSource.FromHwnd(mainWindowPtr);

mainWindowSrc.CompositionTarget.BackgroundColor = Color.FromArgb(0, 0, 0, 0);

http://msdn.microsoft.com/ko-kr/library/ms748975.aspx