When I was a newcomer to Boston, (ca. 1958) it was common for "outlanders" like me to be warned NOT to wear orange, even by accident, on St Patricks day, as it would be construed as "anti Irish" and could result in "aggresive actions" by those wearing the green. I don't believe that those giving out the warning were particularly informed as to the political or religious associations with the orange, but the "real" Irish population there was overwhelmingly Catholic (and mostly members of the police forces?).

I received similar warnings, although less frequently, in Milwaukee, ca. 1965, which is a bit perplexing as the population there appeared to be about 95% Polish (but still largely Catholic, I would presume).

In Milwaukee, again, the only explanation given was that "orange is anti-Irish."

I suspect that in both cases, it was another instance of a prejudice that outlived its own original meaning, although there may have been significant numbers of people in both places who actually held the prejudice and believed that they knew why - just not ones in my circle of acquaintances.

I haven't heard of places in the US where the wearing of orange on St Patricks day is traditional, but it's quite likely that some such places do exist. There are a few places where the main settlers were predominately Irish Protestants, and some others where they were at least a significant fraction of the Irish settlers.

The particular areas where I received warnings NOT to wear orange were most definitely predominately Catholic, regardless of what national heritages might be claimed.

John