I translated two functions from the WinAPI to AutoIt, so we can create transparent windows without any images.
Therefore, we call _WinAPI_SetLayeredWindowAttributes with $i_transparentcolor set to the bg-color of the GUI and ... the background is gone
CODE#include <GUIConstants.au3>
#include <Constants.au3>
#include <WindowsConstants.au3>
#include <WINAPI.au3>
;############# Constants ##########
Global Const $LWA_ALPHA = 0x2
Global Const $LWA_COLORKEY = 0x1