Perhaps you should check out the surrender roll of the 5th Alabama Bn., which was prepared by YANKEE officers at Appomattox. It clearly contains 4 un-named individuals who are listed simply as "Colored Soldier".

You may also be interested in one John J. Jenkins, a FREEMAN from Issue, MD. who crossed the river of his own free will in 1862, proceeded to Fredericksburg, VA and signed up for a 1 year enlistment in the Fauquier Light Artillery. After having seen combat in the Peach Orchard at Gettysburg, his enlistment ended. At this time he re-enlisted in the 3rd MD Artillery, with whom he served until Appomatox. His records are on file at the National Archives in D.C. According to relatives, he was extremely proud of his service and kept his uniform until his home burned during the 1920's.