Q.- Anyone know, who had the best winning percentage record, with the black pieces, in history. {include your source reference, if U know}.
 
Ans.- I dunno, I expect it might be the same guy who had the best % with white.
 
If you mean somebody who did relatively better with Black than White; {Wha-?; 'If you mean'?!!; 'P.G.'}.. American master Weaver Adams comes to mind, he had a + Black score, and a - White score, over his career.
 
The he went on, to write a book: "White to Play and Win"; Go figure!?