The Army of Mississippi as established in 1861 prescribed uniform regulations a follows:
Full dress: Gray frock coats were to be of U.S. regulation cut, but of double breasted design for generals and field officers. Generals' cuffs were plain, collars were black velvet with 2 rows of 7 buttons.Company officers had collars and cuffs of their respective branch colors, with silk braid running horizontially across 9 buttons. Enlisted coats were similar but with worsted braid. Branch service colors were: Crimson for Infantry and rifleman: Yellow for Cavalry: Orange for Artillery.
Trousers were gray with black cord stripes for generals, and 1 inch cloth stripes for all otgers.Black for field officers, and branch of service color for all others. Hats were of black felt, broad brimmed and looped up on three sides. Included were plumes of corresponding branch of service colors for company officers and enlisted men. Plume colors for the following existed:
Brig. Gen.-------Red tipped white
Regimental Field and Staff----Crimson
Adjutant Gen. Corps------Yellow
Quartermaster Gen. Corps-----Blue
Ordinance Corps---------Blue tipped with red
Officers--Dark blue shoulder straps with gold borders
Major Gen.---Gold Star
Brig. Gen--silver star
Lt. Col. Gold leaf
Captain-2 gold bars
1st Lt.--------1 gold bar
2nd and 3rd lts- none
Enlisted ranks paterned after federal insignia.
For fatigue, enlisted men wee to wear flannel shirts with a white star on each side of the collar. Shirts for Infantry were to be red: Gray for artillery: Blue for Cavalry.
Thes regulations were short lived due to shortcomings of the supply system. In thos first days each separate unit had its own uniform and this became a logisitical nightmare.
Thus in 1861...an artillerymn's uniform as prescribed my Miss. Regulation would be...Gray frock coat with orange trim. Gray trousers with corresponding orange trim....Black felt hat with branch of service colored plume. Gray fatigue shirt.As the war progressed and units served in various departments uniforms became generic. Units serving in Virginia were poorly supplied and hteir appearance took on that of other units serving there. Generally 9 button shell jacket and trousers of either wool or jeans cloth, depending on availability. Units generally accepted the uniform of whatever depot supplied their area of operations. This could be somewhat haphazard.
If the individual's unit is known, I would be glad to research the uniform at the given period.