John W. Buckner appears on the 1870 of Sumter District SC as age 39, a cotton gin maker. The service record for him with Co. "I", 1st South Carolina Artillery does match, with the additional note that he deserted on Oct. 19, 1864.

There is no indication in the record that this man was anything other than a white soldier. In other words, no one would think otherwise without the information which you provided.

When information about race does appear in a Confederate service record, and that's rare, it's usually negative. By negative, I mean that it's cited as a cause for for a soldier's discharge.