Some books of interest,
"A Soldier's story: The Records of Hubbard Pryor, Forty-fourth USCT."
Trudeau, "Like men of war, black troops in the Civil War, 1861-1865."
I have searched the internet and google books and nothing mentioned on the flag captured.
I did come across the 8th USCT lost their "National Flag" at the battle of Olustee, Florida.
Source: Black soldiers in Blue: African American Troops in the Civil War Era. By John David Smith.
Have a good a good morning,
Shawn Prouty