I don't know about Fold3, but I searched the NPS Archives, and found the soldier listed in the 3rd USCT Heavy Artillery, Company M, as MELGAR Ward (note spelling of given name. The listing also notes that an alternate spelling, MILGAR, was used). Civilwardata.com repeats the given name as MELGAR.
Looking at the book listing that Fairfield provided, all the Ward folks in the photos appear white. Few privates in colored units were white, but it did occur. Possibly Melgar was an African-American who took the name of M.M.Ward's father.