Yet another reason for there to be a more nuanced difference between Jedi Knights and Jedi Masters. The Tatooine farmer garb would signify a Jedi Master who would be more humble and pursue the ways of teaching and peace. The black clothing would be the uniform of the Jedi Knights in service to the Old Republic, warrior monks who wield laser weapons and do battle with evil. That way, Anakin’s choice to shed his black appearance and reappear in humble peasant robes would signify that he has chosen the role of mentor to Luke like Ben and Yoda have done, while Luke is still wearing the black of the Jedi Knight.