http://forum.xfce.org/viewtopic.php?id=7295 was a similar question. The MediterraneanNight theme currently only has a dark version for GTK3 but it will proximally have a GTK2 version too. I don't know how Darklooks looks. If it's black/blue then you could extract MediterraneanNight's gtk-3.0 folder into the Darklooks folder.