All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
"Abu Tharr, may Allah be pleased with him, was not of African descent. He belonged to Banu Ghifaar, a branch of the Kinaanah tribe that included the Quraysh tribe. His name was Jundub ibn Junaadah. He was one of the earliest men to convert to Islam. He went to see the Prophet in Makkah and converted to Islam there. He was the fourth of four, as only three persons converted to Islam before him." [Briefly Excerpted from Al-'Isaabah fi Tamyeez Al-'Isaabah by Al-Haafith Ibn Hajar, and Siyar A‘laam An-Nubalaa' by Al-Haafith Ath-Thahabi]
It is said that Abu Tharr was dark-skinned. Ath-Thahabi said in A'laam An-Nubalaa', "He was Aadam (dark), big-bodied, with a thick beard. He was devoted to asceticism, honesty, knowledge, good deeds, and he bravely proclaimed the truth with no fear of the blame of any blamer. He was quick-tempered."
Ibn Faaris wrote, "The Arabic adjective Aadam means dark in color." [Mujmal Al-Lughah]
Allah knows best.