فِيهَا اثْنَتَانِ وَأَرْبَعُونَ حَلُوبَةً سُودًا كَخَافِيَةِ الْغُرَابِ الْأَسْحَمِ
In it are forty-two milking she-camels, black like the concealed flight-feather of an intensely black raven.
The word sūdan already communicates blackness. What remains unspecified is the degree of that color. Ka-khāfiyat al-ghurāb al-asḥam makes the deep shade more precise.
The chief purpose is therefore stating the degree of a known quality, not merely informing us that the animals are black.