While following the history of an ex Royal Airlines 757, I came across these two photos which shows a slight variation in the livery. (hint: star-spangled banner)
Photo © Ben Wang
Photo © Tom Turner
In a Civ-Av thread (http://www.airliners.net/discussions/general_aviation/read.main/1672058/6/), someone indicated the plane had some mx issues. I imagine the livery update occurred during the down-time. I also wonder why the slight change...