If the story is set in an area like where you grew up, then I don't understand this question. There are lots of all white trios. Ron/Hermione/Harry, frex. If your story is set in the 23rd century and everyone speaks Chinese, but there are no Asians, then it might be problematic.

If you're uncomfortable writing about people from other races, because you haven't spent much time in racially diverse areas, then maybe just get out more. Go to places near where you live where you can interact with people who don't look like you. You're not a kid anymore. You're not confined.