The reason for the dark complexion is that over time, from the fall of the Umayyad state until the rise of the Funj state, a period of about 750 years, these foreign princes must have married African women. This influenced their complexions, temperaments, and traditions, leading some researchers to doubt their Umayyad Arab lineage or their Arab origin from the southeastern Arabian Peninsula.

The Scottish Englishman James Bruce was the first to attribute the Funj to the Shilluk, in an attempt to kill the Arab and Islamic spirit in that region of the African continent. However, this contradicts the long wars that the Funj waged with the Shilluk kings, from whom Bruce claimed the Funj originated, as well as their fighting with the Nubians. Therefore, James Bruce's statements lacked scientific accuracy.

There are Sudanese acknowledgments that the Funj were a group of Black nomads (some Arabs who acquired blackness from their long stay in Sudan for a long period), who were famous for cattle raising. The historian Yusuf Fadl (from Sudan) states that the origin of these Funj groups is unknown, but it is widely believed that they came from the Upper Blue Nile, from the direction of Eritrea, and established their kingdom in 104/890 AD, after they collaborated with the Arab Abdallab tribes who seized power after they succeeded in overthrowing the kingdom of Soba. After the Funj founded Sennar, they were able to cooperate with the Abdallab and their followers from Arabs, Arabized tribes, and other patriots. Even during the three centuries, the Funj kingdom expanded to include large parts of the Beja country and Kordofan, and their southern borders remained around latitude 23 degrees North. From then on, the Abdallab controlled the villages in the part north of Arbaji, with the assistance of tribal leaders, on behalf of the Funj.