No such thing. Mixed people don't look full black and don't look full white. They look in-between. If you mean they have light or pale brown as opposed to dark brown or more pinkish skin, well, that is just how color works. If you're talking about eye color, brown eyes in every group (white, Arab, etc) always show more. However a biracial person is always half white/black and will always show it in their phenotype (nose, color, bone density, body shape, etc). At base, if you line up 100 blacks and 100 biracials and 100 whites, you could distinguish between the group by looking and measuring their features. The biracial phenotype. will generally come up intermediate between the blacks and white. Like, if you measure a biracial's bone density, they will come up not as heavy as blacks but not as light as white's. If you measure their hair texture, it will come up not as curly as blacks and not as straight as whites. Even their behavior is intermediate. This is what tests have shown for years.