There's a very good photograph of a member of the Medical Staff Corps from the period of the 1st Sudan Campaign on the excellent Soldiers of the Queen website, see http://www.soldiersofthequeen.com/page6 ... 884-5.html
Just to put you on the right path on a couple of things:
I'm not up on campaign uniform, but the RAMC was not formed until 1898 - before that it was the Army Medical Department.
The Army Medical Department was formed in 1873, when the regimental surgeons system was done away with. However, the other-ranks came from the Army Hospital Corps, which existed from 1857 until 1884, and from 1884 until 1898 the Medical Staff Corps. The Medical Staff Corps & the Army Medical Department merged in 1898 to become the Royal Army Medical Corps.
If you are referring to the first campaign, I believe the docs wore the same as the regiment they were attached to, as in those days they were part of the regiment, not part of a separate corps. That said, they probably wore what they wanted.
As mentioned in my above reply the system of regimental surgeons ceased in 1873, from that time on officers of the Army Medical Department wore their own uniform rather than that of the unit to which they were attached.