First off a confession: not only am I white, I'm raised in farm country white where the most diversity we had was when the migrant workers came up from Texas for the summer. My elementary school had maybe one non-white kid in all of K-8. So I wasn't brought up in one of those multi-ethnic rainbows. I'm not really one then who should preach much about diversity, but here are some examples of diversity in my books.
The book Forever Young--published under another pen name--is another lesson in tolerance. The main character Samantha Young is Hispanic and washes up on an island populated by white Puritan kids who frequently call her a "savage" until she proves herself to them. So the whole thing is about respecting people for who they are not their skin tone. (Spoiler!) Later she falls in love with a white kid, though the interracial thing is never brought up.
My short story collection The Carnival Papers--being featured on Wattpad today--has a couple stories involving diversity. In "Learning to Fly" a suburban white girl's car breaks down and when a black tow truck driver shows up to help, she's immediately suspicious of his motives, despite how benign they are. In the story "Flight" a suburban black guy starts to panic when he takes a wrong turn and ends up in the ghetto.
In the novel Where You Belong the primary characters are white but an important secondary character named Roble Madore is from Somalia. He befriends Frost, the main character, when they work together to turn his journey from Somalia to England to America into a novel. Of course besides skin color the book is also diversity in terms of sexual orientation.
In the second book of the Chances Are series, Second Chance, Stacey Chance gets Chinese DNA spliced into hers and ends up as a little girl named Stacey Chang. (Spoiler) She remains partially Asian until about halfway through the third book when she becomes a white man again, but there's a scene near the end of the book when Stacey--now back to Steve--confronts a guy who writes a white supremacist newsletter while searching for a serial killer known as the Skinhead Strangler who preys on minorities.
You might complain that there isn't much diversity in the Girl Power series, but I blame the comic book companies for that one. It's not my fault Superman, Batman, the Flash, and Aquaman are all white. Though really that book is largely about diversity in terms of gender--and sexual orientation--rather than skin color.
There are probably some more examples that I can't remember at the time being. Though I will admit that I default to white characters, see above upbringing. I'm also not the type who feels the need to have a token minority character, unless someone harps on me about it and then I might acquiesce, but it's not really a big deal for me. Unless there's some special reason for it, skin color doesn't really matter, just like religion or any of that other stuff. But the one thing I will promise is that if a character is gay you will know it; none of that cowardly JK Rowling stuff of saying a character is gay years after the fact. That's weak sauce.