Yes Ged, they are all wearing their regulation braided jackets, though the tall guy on the right of the first row appears to be wearing a greatcoat - hard to say given the low resolution as this is the much blown-up scan of a very small pic. Since this was obviously a review of some sort, the men are wearing their jackets buttoned up. In the field however, they probably did unbutton them in the heat of the day - but definitely not at night when it got much colder.
Re-checking my sources, they confirm that the Corsican was abandoned after a few weeks for operations in the field, the men only wearing covered kepis after mid-1866. The hats were put in storage but may still have been worn for the occasional parade.