Years ago, before the Jefferson Davis Museum was damaged in the Katrina, I took photos of a reproduction Mississippi regulation uniform on display. It was a very dark grey, almost black, jean material. Almost all frock coat examples I've seen have the horizontal (about a 1/2 inch in width) black ribbons, some were red in color, across the breast, even with each row of buttons. In photographs of the time they stand out against the lighter coat material. There may have been black frocks in some companies but I have no memory of them from my references.

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David Upton