Discussions over color in Period photographs tend to be controversial. However, there are threads that have done "comparative" analysis of the photographic medium and how different colors are reflected or aborbed, or radically change there black-and-white versions (such as what happens to yellows and reds appearing dark or black.)
I would guess that the dress coats were infantry with the "saxony blue" piping trim.
Shortly after the War, the Quartermaster Department was stockpiled with surplus uniforms. Oh, another outcome of that was they took the infantry dress coats and sometimes removed the skirts making them a form of shell jacket for the cavalry. (Some of Custer's troopers at the Little Big Horn in 1876 were still wearing them.)
In gleichem Schritt und Tritt, Curt Schmidt
Not a real Civil War reenactor, I only portray one on boards and fora.
I do not portray a Civil War soldier, I merely interpret one.