Comment 222 for bug 403135

In my case :
Lucid Lynx 32bits, default theme, nVidia card with Xinerama enabled : all (as far as I know) apps in the notification-area have a white background. (If Xinerama is disabled, the bug disappear in my configuration...)

I've tried to fix this by modifying the source code of gnome-panel (see attachment) : I commented out things in applets>notification-area>na-tray-child.c>na_tray_child_realize(GtkWidget *widget) in order to always use the default "alpha drawing mode" (it is said that "the icon will sit on top of an ugly gray box"). This worked for me, and for other people. See http://ubuntuforums.org/showthread.php?t=1427968&page=5 post #48 (I'm seb_42) for more information.

However, in my configuration, this fix seems only to work for the default theme. So it's clearly not a clean solution, but I thought I had to post my "modifications" here, in case it can help.