Although I have not found the authenticity of this hadith but I can answer the second part that "blackness is a disease"
"Blackness is a disease" is just a point of view of Al-Qaeda leader Hamad bin Hamoud Al-Tamimi. Because
Firstly, Holy prophet in his last address on Hajj has mentioned that
"All mankind is from Adam and Eve, an Arab has no superiority over a non-Arab nor a non-Arab has any superiority over an Arab; also a White has no superiority over a Black nor a Black has any superiority over a White except by piety and good action." 1
Secondly, As we all know that after the flood in Hazrat Nooh 's era, the human race started again with his three sons and black people were the descendents of Hazrat Nooh a.s second son Ham.
Thirdly, Prophet Muhammad (pbuh) said that "“Allah created Adam in His image".
(Al-Bukhaari:6227, Muslim: 2841).
"O people, We have created you male and female and made you into nations and tribes that you may know one another. Verily, the most noble of you to Allah is the most righteous of you. Verily, Allah is knowing and aware."
(Surat al-Hujurat: 13)
In fact, Allah created different skin colors and languages as a sign of His creative power. Just as flowers come in many different colors, all as different divine signs in Allah’s creation, so do human beings come in different colors.
"Among His signs is the creation of the heavens and the earth and the diversity of your languages and your colors. Verily, in that are signs for people of knowledge."
(Surat al-Rum: 22).
"Verily, Allah Almighty created Adam from a handful which He took from the earth, so the children of Adam come in accordance with the earth. Some come with red skin, white skin, or black skin, and whatever is in between: thin, thick, dirty, and clean."
(Sunan al-Tirmidhī: 2955).
Hazrat Bila r.a has such a high rank that he was the first mu'azzin (prayer caller) in the Muslim faith and he also belong to the black race.
So, Righteousness is the only quality that makes someone virtuous in the sight of Allah, not race, or skin color, or lineage, or social status, or country of origin.
- The Last Sermon of prophet Muhammad(SAW). (n.d.). International Islamic University Malaysia.https://www.iium.edu.my/deed/articles/thelastsermon.html