Messieurs !
One must also note that those high scoring pilots often had several machines. The Luftfahrtmuseum Berlin showed one Red Baron Triplane before WW2; it vanished after WW2.
In the books I never found well researched facts on where those colourfull markings were painted on but I think it is rather unlikely that it was done at the factories.
In the German Army there was a system of parks for refurbishing and in-deep repair jobs and in the field there were workshops for the equipment: tanks, blacksmiths, aircraft, trucks, cars,
rolling stock, locomotives etc. and therefore I think it was done in the field.
kind regards, Gunther