I grew up in an area that was racially and ethnically diverse. Socioeconomically, maybe not so much, but race and ethnicity? Yeah.
I graduated from a college where the majority of the student body was Protestant, caucasian, and heterosexual. Experiencing that social culture versus the one I grew up in was like a slap in the face. Everyone claimed tolerance and acceptance, but underneath? It wasn't there. Homophobia was rampant. (I'm sure several people know about UVA's fight song and the disgusting "tradition" to alter a lyric to "not gay.")
And the race issue? The newspapers liked to ask the question of "Why do all the minority kids hang out together? Why do the black kids hang out with the black kids? Why do the asian kids hang out with the asian kids? Why do none of them hang out with the white kids?" Note, though, that the onus here is on the minority kid to approach the white kids. Because based on my observations while a student there, I can count the number of times on one hand that I saw a white kid approach the black kids or the asian kids. And I'd have fingers to spare.
It can a daunting task for that minority kid to approach the white kids -- especially when none of them extended an invitation and in certain circumstances, made it very clear in every single way except for verbally, that You Are Not Welcome.