Here’s an exercise that illustrates – in one small way — the difference between being black and white in America. Take a roomful of college students, half black, half white, and ask a young black woman if she knows the song, “Lift every voice and sing.”

She will usually look at you the way she would if you asked if she had ever heard of Woodward Avenue.  Then turn to a white student about the same age and ask the same question.

They will almost always give you a blank look.  Ask another pair, and then another, and you will keep getting the same result until everybody is stunned, and looking at everybody else.

The black students are mostly shocked that almost none of the whites have ever heard of that song, a song that sometimes is still called the “Negro National Anthem.”

The white students are mainly bewildered. Then both groups finally get the point.  Black people have to live in two cultures, two worlds, theirs and the majority white world.

On the other hand, white people can get by living in only one.

Welcome to what the Swedish economist Gunnar Myrdal called “An American Dilemma,” three-quarters of a century ago.  We’ve come a long way since then. Legal segregation no longer exists.  We’ve elected a black president – twice.

Yet it is still amazing how few white people have black friends, and vice-versa.  I don’t mean somebody who you say hello to at the office. I mean real friendships, where you actually know each other.  Mike Rott’s magnificent film, Luft Gangster, was done to celebrate a true hero, but also shows what the consequences of racism have been for our society.

It begins by showing what the army officially thought of African-Americans when World War II began, how it was set down in writing that blacks had physical strength, yes, but neither the intelligence nor the courage needed to be true warriors in battle.

Long before the end of the movie, we realize that whoever wrote those lines probably isn’t worthy of being in the same room at Lt. Col. Alexander Jefferson.

Not everyone is a bigot or a war hero, however, and Whitey Daniels and Cookie Marsh have written a book that shows all of us the most important thing we can do for the future of this country: Talk to people. Just talk to them.

Who knows? You might become friends.  That’s what these two aging baby boomers did, pretty late in life.  That doesn’t mean either group has to abandon its own culture.

What it does mean is realizing that we are all in this together, and we need to resist so-called leaders, whether white or black, who attempt to divide us for their own political purposes.  Bob Dylan had a song a long time ago called “Only a pawn in their game,” that told how the rich stirred up race hatreds in the hope that poor whites wouldn’t notice that they, too, were getting screwed. My guess is that millennials are less hung up on race than older Americans.

But we all still have a long way to go.  Rodney King’s famous question, “Can we all get along?” is as relevant as ever, but it doesn’t mean just tolerance, and failing to beat up or shoot people who don’t look like you.

It means getting to know each other. Tom Daniels and Tom Marsh have given us a blueprint; Mike Rott and Alexander Jefferson have given us a role model.

So let’s live up to the promise of this nation at last.