Never heard that before, and I have been a Luftwaffe researcher, historian and author for 48 years. It always seem to me that it was more a function of success in the air rather than nationality. The more successful the pilot - be he German or American - the more latitude he had in the realm of personal markings. Another factor was the personal taste of the pilot's Staffel (squadron), Gruppe (group) or Geschwader (wing) Kommandeur (commander). Some didn't care what personal markings their pilots applied, while others were very restrictive. Additionally, both air forces had policy directives/regulations on the application of personal markings and these had a large influence on what the commanders allowed.
So, to answer your question more directly, I would say that your statement is NOT true.