It's not only the Royal Gallery which has its undiplomatic reminders of past enmity between France and Britain. I once took a group of French students from Poitiers around the Palace - one was really impressed to see the coat of arms of that French city in a window on the stairs up to the committee corridor. Of course it turned out that this display of such symbols was a reminder of battles in which the English (or British) had defeated the French.
The Palace was decorated during the mid 19th century - and reflects the then current feelings. America comes off much better. By the time the new Palace was constructed we had got over the Declaration of Independence and the bad feelings of the early part of 19th century. There are paintings of the Pilgrim Fathers (an irony since they were political and religious refugees from England) and other images of our shared history.