You are the first person I've read on this subject who has helped me to really understand it. As a middle class white person, I think of it more as class privilege. People tend to hang out with people they feel they have something in common with.
I have been fortunate enough to meet lots of people who don't look like me who have become close friends. That's because we shared a common faith and worked together in a church where we had chance to really get to know each other on a heart level. I was a minority in that church.
On the other hand, there have been many white people I never really wanted to know because I assumed we had nothing in common. I think I will write a post of my own to expand on this. I hope I can explain it as well as you did. And you're welcome at my house anytime if you ever make it to California.