How do I make a transparent deskband?

See more:

C++

Windows

ATL

buttons

Taskbar

Hi All, i realized an ATL deskband based on a button
(like "Tablet PC input panel" of Windows 7)
but when shown it looks like a grey button.
I'd like to make it transparent (like the windows one)

here my code

CWindow deskband;
deskband.Create( L"button", hwndParent, CWindow::rcDefault, L"deskband", WS_CHILD | BS_ICON );

HICON hIcon = reinterpret_cast<HICON> LoadImage(0, IDI_EXCLAMATION, IMAGE_ICON, 0, 0, LR_SHARED));
deskband.SendMessageW(BM_SETIMAGE, IMAGE_ICON, reinterpret_cast<LPARAM>(hIcon));

thanks
dario