Could be a pre-war militia jacket, maybe? Certainly Louisiana militia often had blue outfits when "war were declared." Ohio, Indiana, New Hampshire, New York, Massachusetts militia in gray, Georgia and Louisiana militia in blue, that kind of thing?
Of course, it is a black and white ambrotype or early photography, so maybe it is "cadet gray" versus one or another shade, and just looks darker in the picture? Interesting photo... Sergeant vs. Sergeant major? Any evidence that officers and or senior NCOs had a different color until the multiform became more uniform?