I read a secondary explanation for this marking scheme was that French feelings were still running a little high over the RN's bombardment of the French naval base at Toulon in July 3, 1940. The Germans capitalized on this necessary bombardment for propaganda purposes and used the Vichy French government to do so. The Vichy French govt ran French Morocco and Algeria where the Torch landings were to occur. It was felt by the Anglo-American leadership for the landings the French defending the landing areas would have less likelihood of firing on British aircraft from the ground - or fighting them in the air - if ALL aircraft involved in the landings used US insignia. There was no animosity against the Americans among the French at this time.
I know there were minor instances of the French resisting the American landings at isolated spots, however, that happened because the French units involved felt honor demanded they at least make a show of resistance. It was not motivated by specific nationalistic animosity against America or American units.