Ambrose of Milan

It is written, "Ethiopia shall stretch out her hand unto God." In this is signified the appearance of holy church, who says in the Song of Solomon, "I am black and comely, O daughters of Jerusalem": black through sin, comely through grace; black by natural condition, comely through redemption, or certainly, black with the dust of her labors. So it is black while fighting but comely when it is crowned with the ornaments of victory.

On the Holy Spirit 2.10.112 ↗

Jerome

Born, in the first instance, of such parentage we are naturally black. Even when we have repented, so long as we have not scaled the heights of virtue, we may still say, "I am black but comely, O daughters of Jerusalem." … "For this cause shall a man leave his father and his mother and shall be joined unto his wife, and they two shall be" not as is there said, "of one flesh" but "of one spirit." Your bridegroom is not haughty or disdainful; he has "married an Ethiopian woman." When once you desire the wisdom of the true Solomon and …

Letter 22.1 ↗

Gregory the Dialogist

We know that in the beginnings of the Church, when the grace of our Redeemer had been preached, some believed and others did not believe; but those who believed were despised by the unbelievers, and having suffered a kind of persecution, were judged to have departed, as it were, into the way of the Gentiles. Whence the Church in those same persons cries out against those who were not converted: "I am black, but beautiful, O daughters of Jerusalem." I am black indeed by your judgment, but beautiful through the illumination of grace. …

Commentary on the Song of Songs, Chapter 1 ↗