From
https://bugs.launchpad.net/ubuntu/+source/amule/+bug/115341It looks like the aMule tray icon is not always transparent, at least in KDE:
http://launchpadlibrarian.net/7689727/snapshot20.pngFrom the last comment:
"It appears that the aMule tray icon becomes transparent only on the desktop on which aMule has been started.
When you go to another desktop (with another wallpaper), the icon is no longer transparent.
The reason for this is that the transparency "screen shot" was taken on the other desktop and the icon does not become updated when the desktop wallpaper is changed."
I don't use KDE, so I can't check it. But it doesn't happen with Gnome.
BTW, it's with 2.1.3, but the trunk changelog doesn't mention any tray icon change.