This essay explains, in four topics, that much is known about the heredity of those physical features important to U.S. society in assigning someone to one side or the other of the endogamous color line. Three-to-Six Co-Dominant Skin Tone Genes discusses the genes that determine skin tone. Mendelian Inheritance explains that, on average, half of the children of admixed parents inherit a skin tone between those of their parents, one fourth come out darker than both parents, and one-fourth come out lighter than both. This means that any Afro-European admixed population will not blend homogeneously after many generations, but will continue to produce a few African-looking and European-looking individuals indefinitely. Appearance is not the Same Thing as Ancestry explains that, in admixed populations, even people who share identical ancestry may wind up with different Afro-European admixtures due to the random recombination of parental genes at each generation. This is why about five percent of the African-American population has no detectable African genetic admixture. Finally, Hardy-Weinberg Distribution shows how to compute the rate at which European-looking children are born into various Black communities in the United States, and the rate at which African-looking children are born into European-looking populations in other countries.