I added a response, but there was a character limit, so I want to make my own post and LJ still strikes me as a better location for a wall o'text:
I was curious enough to take a quick Google, and first off, Wikipedia claims Tony Stark's mother's maiden name was Maria Collins Carbonell, except in the Ultimates where she was Maria Cerrera.
Searching "Maria Carbonell" turns up several real-life individuals named María Carbonell, all of whom appear to be in or from Spanish-speaking countries. I then tried searching "Collins Carbonell," and got someone in Chile named "(Firstname) Carbonell Collins." I leave out her first name because I worry that I'm being a bit stalker-y, looking up all these people.
So, we've got a possible Spanish or S. American connection, even with the middle name “Collins.” Is there a cannon backstory for how Howard and Maria met? I assume that in the movie universe at least it was after WWII, as Howard Stark appears to be single during the events of Captain America. The Carbonells could have been a Spanish family opposed to Franco, but the "Collins" part of the name makes me guess a Latin American connection: I can see Cold-War Howard Stark doing business in South America, both for its own sake and to guard US trade interests, and I think it would be completely plausible for a wealthy family there to have a 19th-century trader or gold prospector named Collins in the family background.
copperbadge points out that Stan Lee originally wrote Tony as coming from a privileged background, which at the time would not likely have been Italian-American; but AFAIK, up until, say, the Cuban Revolution, American reaction to an industrialist marrying a (wealthy, light-skinned) Latin American bride would have been something like "ooh, she's so exotic and sophisticated."