Whilst it doesn't directly address your question, this earlier answer by u/cleopatra_philopater may be of interest (as may some of the quotes from Mary Beard in the article linked by the OP): [Given the recent furore concerning Dr Mary Beard, I wondered if there are any official accounts of black Roman officers or any records of census' carried out in Romain Britain to give an idea of the homogeneity of Britain at that time?] (https://www.reddit.com/r/AskHistorians/comments/6s918x/given_the_recent_furore_concerning_dr_mary_beard/)