First off, communities were much more segregated. So if you were a White person going to a public school, chances were that you lived in a White neighborhood and all your classmates were white. That was even true in NYC when I moved back to Flushing in 1967. The neighborhood was still mainly Italian & Irish, with a few Greeks that had immigrated post-WWII.
After Vietnam in the 1970s-80s however, Asians started moving en masse into Flushing, and by the time my mom sold the house in 1996, the white folks were moving to Long Island and the neighboehood was at least half Asian. Today, Flushing is the biggest "Chinatown" in the world, and bigger than the original NYC Chinatown in Manhattan.
Far as Muslims go, I don't ever remember seeing a woman wearing a Hijab on the street in those years. Migration from Africa and MENA didn't really pick up until after the Gulf War in the 1990s. Immigration from Europe slowed down as their Birthrates dropped, and to keep the numbers up and Cheap Labor flowing in, immigration to the FSoA since the Millenium has been nearly entirely Brown or Asian people which have been dispersing all across the FSoA and into many formerly Lily White communities.
The second major reason is the perception you get from the Media. Right up through the 1990s, TV shows generally featured All White casts whether they were Sitcoms or Dramas, except for the shows directed priimarily towar a Black audience like The Jeffersons or Sanford & Son. Today, no shows EVER have an All White cast, they are always nicely WOKE with mixed race couples and a Rainbow of kids including adoptees to make sure a couple with a White Dad and Black Mom has a Korean son and Egyptian daughter too. lol. Their next door neighbors are Lesbians in a mixed religion Hindu-Jewish combination with a Nicaraguan son who joined a Hare Krishna for Jesus cult. lol.
I didn't really notice how much the general complexion of Amerika had changed until I moved up her in 2007 and did my first 4th of July Parade. Alaska was one of the last holdout Lily White states. 3 miles of all Caucasian with the occasional Native watching the Parade.
RE