More on the relationship between the blackness the people of al Al Zanj and the people of the Hijaaz (Arabs in Mecca, Medinah, Taif, etc)
Al AnSaab li Samaani Chapter 3 Page 170
And it is said that Muslim Ibn Saeed Ibn Jarjah and he was from As Shaam (meaning Roman here) in origin and he was a beautiful white complexion
….And he was only called Al Zanjy because he was white with some redness (very white skinned) for this reason they called him Al Zanjy to mean the opposite because the people of Al Hijaaz had As Sumarah in them
ويقال مسلم بن سعيد بن جرجة، وأصله من الشام، وكان أبيض مليحا
روى عنه ابن المبارك والشافعي والحميدي وأحمد بن عبد الله بن يونس، وإنما قيل له: الزنجي لانه كان أبيض مشربا بحمرة فلذلك قيل له: الزنجي – على الضد لان أهل الحجاز فيهم سمرة
Again we see here Asamaani may Allah have mercy upon him makes record of the understanding of As Sumurah and how it was used to mean blackness and that it is a complexion opposite to the whiteness of the Persians and Romans and that the people of Al Zanj fit into the category of As Sumurah similar to the Arabs!