The message of this manga did strike me as heavyhanded at first, but I sorta reconsidered. Most kids in the US couldn't care less about your race or hair color, and viewing it from that lense the reactions in the story are pretty unrealistic. On the other hand, Japanese schools can be brutal. There are a few news articles you can find about dumb things they've done in the name of conformity. It's a cultural issue that isn't really relevant to most native English speakers, which does make it seem preachy.
The story is pretty good otherwise