Historically, in the US, race has been a combination of phenotype and genotype.

Phenotype refers to visible physical characteristics, such as skin color, shape of the nose and lips, texture of the hair, stereotypes about body shape: for example, the stereotype that African women have big breasts while European women ate flat chested. Or the stereotype that Europeans have flat behinds while Africans have more round behinds.

Genotype refers to one's genetic makeup or background, or ancestry.

In the US for more than 400 years, the state laws practiced hypodescent. It meant that one drop of supposed black blood or ancestry made one black. In colonial Virginia and North Carolina, and many other states, a person was classified as Negro if he had one-eighth Negro blood or ancestry. This meant to the third generation, from parent, to child to grand child to great grand child. One black great grandparent made you black or colored. Mixed race was mulatto, and mulatto in the US was NOT white. The most extreme case of this obsession with white purity was in Louisiana. Down until the 1970s, Louisiana classified a person as colored if he or she had any traceable amount of colored ancestry. Then they liberalized the law to define colored as more than 1/32^nd Negro blood. This goes back five generations. The racial classification is given on the birth certificate, under state law. And as late as 1967, some 16 states forbade interracial marriage, until the Us Supreme Court ruled these laws unconstitutional.

Hypodescent means that any degree of ancestry from a particular group trumps or takes precedence over all other ancestry. In America, black or African ancestry took precedence for at least three generations and made you not white. Theoretically it could have worked in reverse. One drop of white blood or ancestry could have trumped everything else and made you white. But in 400 years America has never, ever, practiced white hypodescent. It has always practiced black or African hypodescent.

But what is hypocritical is that white Americans who live in a society that for 400 years utilizes the one-drop rule to define anyone with a single "drop" of African blood as black then say that the Egyptians are not "really" black because they are brown and they are mixed and they may be partly Semitic like the Arabs. By the logic of hypodescent, everybody in Egypt is black, although not necessarily as dark as sub-Saharan Africans. And if mixture makes the Egyptians not "really" black, then half of the so-called black Americans in the US are not "really" black either. One cannot have it both ways. If race mixture makes you black, as it has in the US for hundreds of years, then it makes the mixed race Egyptians black too, in the sense of hypodescent. Mariah Carey is not dark, but her father is black and in the US that makes her black. Vanessa Williams is not dark, but in America she is "black."