Actually, I didn’t mean skin colours. There are quite obvious differences in the bone structures in the face of different Asian peoples, which gives it away far before colour does. Admittedly, colour would play a role, however as you said it can’t be relied on. For example, Cambodian upper-class women traditionally have comparatively pale skin.
Chinese people (especially in their homeland, it might not be the same with ex-patriates) would be even more attuned to these subtle differences, and thus it is fairly unlikely that a Japanese person would be ignored.