Question: There is an eighteen-year-old boy who lives with his abusive mother. But he has his best friend of seven years who is Asian and his mentor and his mentor's daughter who are Hispanic. I feel like the characters work, but I don't know if people will feel that I'm putting them in just or the sake of having diverse characters. Am I?Answer:
Are you? You tell me.
If you're not just putting them in to have diversity, if the characters are chosen for specific reasons, why worry about this issue? Very few readers will complain that a story's cast is "too diverse." People who are not interested in learning about a variety of people don't tend to read fiction.
Besides, you cannot write just to please a generic reader, because readers are also diverse. You have to write stories that feel meaningful to you in order to have them be meaningful to a section of readers who respond the same way. The people who would criticize a story for being too diverse are probably not your readership.
On the other hand, if you are including characters because you think you should have diversity, that's not a necessarily a bad thing either. Just make sure you know the characters and cultures well enough to make them authentic. You will want to avoid stereotypes.
Of course, there are stories where the ethnicity of the characters is crucial, where characters of a different ethnicity simply wouldn't work to illustrate the theme or convey the meaning. And there are stories where ethnicity seems tangential or irrelevant to the story.
Only you know which type you are writing.
Best of luck.