The color line is still a central problem in the United States, as Du Bois declared more than a century ago. But economic, demographic, and social trends have subdivided it in ways that Du Bois could not have foreseen, creating tremendous intra-ethnoracial group diversity. A challenge for twenty-first-century scholarship is to make sense of the implications of growing intra-group diversity for the boundaries and meaning of group identity. Meeting this challenge requires treating intra-group diversity not merely as an outcome of various social processes. Intra-group diversity must also be seen as the origin of processes shaping the boundaries and meanings of group identities, as well as intergroup attitudes and relations. Meeting the challenge also necessitates adopting ethnographic and survey research practices that better capture the dynamism of the multiple color lines defining the American ethnoracial landscape and the implication of this dynamism for identity.