Between African American families, darker skin correlates with lower IQ at r=-0.15. Within full biological black siblings, skin color differences show zero correlation with IQ differences. Between black families, darker skin links to lower educational attainment. Within black siblings, skin color unrelated to education differences. Hereditarian theory predicts and confirms skin color proxies white ancestry and IQ genes between families. Skin color cannot proxy ancestry within full siblings due to equal inheritance odds. No evidence for pleiotropy linking skin color genes to IQ genes within families. Colorism fails as explanation since within-family correlations are zero. Cross-assortative mating or white gene flow maintains between-family skin-IQ link. Half-siblings show weak expected skin color-IQ trends due to partial shared ancestry. Step-siblings mimic between-family correlations from assortative mating. Overall population skin-IQ correlation rho=-0.44 ties to white admixture. IQ-education correlation stronger between than within families at 0.645 vs 0.410. Sample supports white ancestry including better IQ genes as mechanism.