Upvote:4
There is a version of this picture that bears the description:
Right Hon. Sir Redvers Buller, V.C., G.C.B., etc.
Commanding in Natal
In the Uniform of Colonel Commandant, King's Royal Rifle Corps
Searching just for the uniform of that unit then lists Buller as a prominent 'search-hit', like Original Rifle CORPS Uniform Pics, and reveals this illustration:
King's Royal Rifle Corps, Officers and Rifleman 1904: