The traditional theme of the prince imprisoned in the tower by his father has a racial twist in Vélez de Guevara's Virtudes vencen señales. Filipo is a Black prince born of white royal parents in a mythic Albania. The noble virtues inherited by this Black heir will become evident even to his enemies, but his black skin delegitimizes his position as head of the realm. The medieval doctrine of biologically inherited virtue and nobility is put to the test in this baroque recreation of the topos of essence hidden in false appearances. The conflict is heightened by the interplay of race and gender, the latter embodied in the white sister of the protagonist, who claims to represent true Albanian and royal identity. Being of converso descent, Vélez de Guevara is aiming, through Black prince—and later king—Filipo, at the social concept of limpieza de sangre, seen by many aristocrats in 17th-century Spain as a negative practice that excluded worthy people from the center of power on purely racial grounds. As in the Black saints' plays written by Lope de Vega and others after him, an inner self overcomes the disqualification of blackness in the skin. The anxiety of black skin pollution remains intact in the end, and the individual worthiness of the protagonist is asserted as an exception to the general rule of the moral debasement of all people of African descent.