Hi MoFed,
You know I have never read of any significant number of Black Confederate troops being captured by Federal soldiers. Maybe they were 1) better at evading captured than their white compatriots or 2) disguised as white men and thus able to fool those Yankees during capture and their years as a prisoner of war (never heard of many of them in those Yankee POW camps either) or 3, there were not that many around. Think, I will pick door number 3.