Let's start with the simplest point about this picture, they are wearing Winter Uniforms. The Confederacy never had Winter Uniforms. Sometimes the Winter Uniforms were such a light blue they came out as grey in black and white pictures, but they were never grey in reality.
The 1st Louisiana Native Guard really did exist, but there are no known photos of them. There are photos of US Black troops that later had "1st Louisiana Native Guard" written on them, but that is different. The 1st Louisiana Native Guard was a free Black military unit that Louisiana refused to authorize, and Confederate General Lovell threatened to execute if they tried to assist the Confederacy during the capture of New Orleans. They were folded into the Union Army.
The white is A.M. Chandler, and the Black is Silas Chandler. The photo was taken before Chandler entered the Confederate Army. The photographer would travel the countryside with fake Confederate uniforms, and prop weapons. For some reason, Chandler dressed himself and his slave up as Confederates, and pretended they were both armed. When he did join the army, his slave did not wear a uniform. His slave carried messages back and forth for him, and after he was injured, his younger brother. His slave, Silas, traveled through Union lines, and was not harassed as an enemy combatant. Silas had his family threatened if he ever tried to be free.
The white family has a lot of stories about AM and Silas being the same age, and being like brothers. Silas was 7 years older than the teenage AM, and had a wife and children. They were always at very different stages of their lives.
Silas' family after the Civil War had a tradition that female members of their family should never have contact with their former owners. I think we can all guess why.