Midii
Argh, it says in the official character info that Heero is Japanese and therefore we know that he is
gonk Right... that's what we were sort of saying. However, just because I'm born in one country, doesn't mean my ancestors couldn't have been born in another.
For example, I had a friend in high school. Her parents were Indian, she was English, and her brother was American. They were all blood related. Your "nationality" is based on where you were born and your citizenship status... not your bloodline.
So, Heero may very well have been born in a Japanese colony (or even on Earth in Japan, we don't know for sure), but his family and/or ancestors could have moved there at some point in history before that, which would explain his non-Japanese looks.