Companions and handbooks are very helpful kinds of sources. They are edited by leading scholars in the particular areas of research, and those editors commission researchers to write individual essays on the subjects which are their specialties. As a result, students get a much better understanding of the issues involved in a particular subject area, since the authors go beyond factual summaries to analysis of differing arguments in the field.
For companions and handbooks involving ethnicity and race, see:
"Ethnic Prejudice and Racism" in The Oxford Handbook of Hellenic Studies (2009)
"Identity" in The Oxford Handbook of Roman Egypt (2012)
Additional relevant material may be found in the series below when looking by Classical author, literary genre, or topic.
Blackwell Companions - 65 Titles
Brill Companions - 35 Titles
Cambridge Companions - 44 Titles
Aryballos in the form of an African's head, Walters Art Museum
Between 480 and 430 BCE (Source: Wikimedia Commons)