Many units in the Civil War, especially the side of the Union, didn't vary much, excluding Zouaves.
The regiments
to come out of New York got a special, State of New York shell jacket.
(pictured below) This had 8 State of New York
buttons along the front of the dark blue shell jacket with sky blue trim. The jacket had two epiletts on the shoulders.
Through the war, the 18th was cycled standard 4 button wool jackets and frock coats. At times, the 18th were so ill-equipted
that some men just had their shirt on their backs.
The trousers were standard Kersey sky blue wool trousers.
Headwear
consisted of a dark blue wool kepi or forage cap.
(Pictured below) In some companies in the 18th, it's
evident that some men wore fezzes. Check out the
Original Photos.