@motorollin
I could be wrong, but no Amiga does Transparency..............what your probably seeing is the menu gets dithered or pixels are eliminted so that you can see through it. Like for example.....grab an icon on the desktop is OS3.9 and drag it around the screen...........you can see through it, but you will also notice it is not as solid as it was before........pixels have been elimintaed......it has been dithered with color zero.
Real TRansparency requires 16 million colors or a gfx card and higher resolution. But I suspect the effect is done the same way........but because the resolution is higher........you cant see the holes and the image would still look pretty good.
Perhaps there is another technique? I don't know...........imnot even sure I am correct on this matter.