Looking at the original photo is certainly helpful. I don't think I can discern a color for the cuffs either, and green is an interesting choice, being associated with riflemen before. I don't know if the man on the left has them or not. I can't really make it out. There are a number of 13th Reserve photos of men in caps. I don't know if that's significant in terms of uniforming, or speaks more to where and when they had their images done. Remember that many of the hat decorations weren't full tails; they were pieces cut off the hide. They never were of anything approaching a uniform size or dimension. As for the gun questions in the drawing, I have come to believe that at that time, the 50s - 70s, uniform illustrators were more interested in showing the uniform than the firearms. The gun is just a prop, sort of like the way men in clothing ads are always holding something to make the fabric drape. I've seen otherwise credible uniform plates that show the lock missing on a musket, or the wrong musket altogether for the unit, or (in the case of a famous reconstruction of the 42nd PA) the lock on the wrong side of a Sharps. In fact, the lock detail on the Sharps in the drawing is pretty indistinct. The only real identifying feature is the shape of the rear of the lock. That really wasn't what they were interested in at that time. For the artist's purposes, it may as well have been a stick.
I get so used to thinking of horns for priming powder that I forget about using them for carrying loose powder! Of course they were still in use. What was I thinking?