The background scene is a screenshot taken at the deepest end of the Shadow Shard, the most beautiful, original, creepy, and shamefully underused area in City of Heroes. Seriously, it's a whole alternate dimension full of floating islands, strange monsters, refugees, mile-wide sky palaces and a bewildered U.S. military/scientific expedition tasked with figuring it all out... and all there actually is to do there are some algorithmically generated cave missions and a couple of immensely long and tedious Task Forces, at the conclusion of which you aren't really any more edified about the place (or so I understand.) It's a real shame, is what it is, and it's also an unfortunate example of the designers' habit of preferring to build shiny new zones -- The Hollows, Striga Island, Croatoa, City of Villains... -- when there still are entire neighborhoods of Paragon City, in there from the day of release, which have always been ghost towns. If I were in charge of CoH I'd be pulling people off new zones left and right and reassigning them to add content and interest to these underused zones instead.
(And, as someone who knows absolutely nothing about how the game is managed or what the player base really wants, I'd clearly be the best person to make such decisions. Clearly. I can't imagine why Cryptic hasn't called me up to ask my advice already. Maybe there's something wrong with their office phones -- that must be it.)