Some color issues
Issue 1: If "Gajim works nicely with GNOME" why not using tango colors? They're soft, clear and pretty. I mean group chats nicknames colors, status messages and in/out messages. Everything, what uses colors must use ones from the [http://tango.freedesktop.org/static/cvs/tango-art-tools/palettes/Tango-Palette.png:Tango_palette].
Issue 2: Most of messengers using usefull messages highlighting, when your message colored with light gray and every other colored by black/dark gray color. That looks really good, why not using it in gajim?