He also included a bare-breasted, sword-swinging warrior angel. Doesn't mean that there were large numbers of them on the battlefield.
Blacks did serve in the Confederate Army. Not as many as in the Union army, but still a considerable number. Dr. Lewis Steiner, Chief Inspector of the United States Sanitary Commission while observing Gen. "Stonewall" Jackson's occupation of Frederick, Maryland, in 1862:
"Over 3,000 Negroes must be included in this number [Confederate troops]. These were clad in all kinds of uniforms, not only in cast-off or captured United States uniforms, but in coats with Southern buttons, State buttons, etc. These were shabby, but not shabbier or seedier than those worn by white men in the rebel ranks. Most of the Negroes had arms, rifles, muskets, sabers, bowie-knives, dirks, etc.....and were manifestly an integral portion of the Southern Confederate Army."
Here's a pic of black confederate pickets from the Northern paper Harper's Weekly:
Frederick Douglas said that:
"It is now pretty well established, that there are at the present moment many colored men in the Confederate army doing duty not only as cooks, servants and laborers, but as real soldiers, having muskets on their shoulders, and bullets in their pockets, ready to shoot down loyal troops, and do all that soldiers may to destroy the Federal Government and build up that of the traitors and rebels. There were such soldiers at Manassas, and they are probably there still."
These are all Northern sources. Go argue with them.