The image is white and transparency is set to 50%, I think. That's all. And for the other elements, I just set background to none and so just the image appears, which is transparent. Really simple.
If you plan something similar, feel free to copy the right.png file and use it by your own ;)
we only have archlinux here at home on both desktop and laptop and we are more than satisfied with it! after reading your About i thought you would be happy to hear that :)