Well battleship gray looks better even when the plane's exterior hasn't been washed. White fuselage without regular washing generally doesn't look very good. Air France used to get ridiculed on other forums for not washing their planes which always stuck out like a sore thumb when it got dirty, especially with the dirt imprint around L1 / L2 door from the jetbridge. United must be doing regular exterior washing, because I've yet to see a plane and go ... yet. Now the interior conditions on United planes is a whole different matter.