The uniform on the right as 90th said depicts a colour sergeant.
I have just asked the seller if he could determine what was on the epaulettes or collar, his response is below.
The uniform is post 1881 and SWB appears on the epaulette of the Corporal. The South Wales Borderers at the time of the Zulu War had green facings but sometime in the 1880's they changed them to white so I would presume that this soldier served with this regiment. Hope this helps.