If the panel has a background image, this image will not be repeated in the background of launcher icons, even if said icons are PNG's with transparent backgorunds. The panel background image *will* fill up the backgrounds of icons within launcher menus however - if these icons are PNG's with transparent backgrounds
Additional information: I've spent a while trying to make my desktop look like MacOSX, and so I've started using a GTK2 theme 'Panther' -- though it looks like Aqua, and consequently has repeating horizontal grey/white lines for the background in windows, menus, and of course the panel's background image. However, despite the fact that all my new pesudo-MacOSX launcher icons are PNG's with transparent backgrounds, the background line image from the GTK theme is only showing up behind launcher-menu arrows, icons *within* launcher-menus, and behind the icons in dialogue windows - but *not* behind panel launcher icons.
I have no idea how to solve this and no time to look into it unfortunately. It may have something to do with the xfce widget not being covered by the theme. If anyone would like to look at this, that would be highly appreciated.
this may be somewhat related to how the xfdesktop menu (using a custom widget) doesn't always follow the theme. i _think_ that can be fixed by calling gtk_widget_set_name(item, "GtkMenuItem") - so maybe setting the name to "GtkButton" here will do the trick. i'll look into it.
ok, patch for libxfcegui4 attached that should fix it (haven't tested, other than that it compiles). jasper, your call on whether or not it's too hacky to commit.
fix applied to CVS.