Star Trek has always been at the forefront of ethnic and cultural diversity. In TOS, we had a Russian, a Japanese-American, a Scot(t), Americans, etc. which was groundbreaking for the time. In the TNG era, we had French, Japanese, (black) American, Native American, etc.
But the most unbelievable thing about this (especially for 400 years in the future) is that they all seem to be mono-ethnic. This seems pretty dated even by today's standards just 20-30 years later, let alone 20 more generations.
As far as I can recall, all the multi-ethnic characters seem to be hybrids between humans and aliens. And the only other exception I can recall would be the children of Keiko and O'Brien, which is more of a development than a starting point.
Have we ever encountered a notably multi-ethnic character? As in, a character just happens to note that they have genetic ancestry from more than one area of the Earth?