In my application I have a form which I tweak by using the DWM API's method DwmExtendFrameIntoClientArea to extend the height of the Aero Glass Title Bar so that part of my form client area is drawn on the Aero frame. To achieve this effect, I also draw a black rectangle on the part of the client area which is 'over' the glass frame so that it appears transparent, as many online articles suggest. This worked pretty well under Windows Vista/Windows 7 but as I downloaded VS 2010 and used the .NET Framework 4.0 as my trarget framework to build my application, this approach no longer works. The problem is that the black rectangle is visible, i.e. the black color is no longer considered transparent when drawing on Aero glass. Does anyone have an idea what might be wrong with that and how it can be overcome?