Aircraft cleaning
Lately, I have noticed airliners that seem to have "patches" or sections of fuselage cleaner or shinier than the rest. This seems apparent on really dirty aircraft where in a small square section, at what seems to be a random place on the fuselage, appear newly painted or newly cleaned.
Is this some cleaning process or a maintenance procedure, perhaps? I would imagine that if the plane was cleaned, but not completed due to a scheduled flight, the clean patch would not look as perfectly square or sectioned. Likewise it seems to appear on random places such as a few rows of windows on the rear of the aircraft, or from a door to a few window rows after, etc.
Any enlightenment on this? Just a curiosity.