Where, Whom and When?

My great-grandfather is one of the soldiers in this photograph.  He lived in Sheffield for most of his life but died in Lincolnshire.

The person who sent the photo to me said that he thought they were Black Watch soldiers.  Not so, and they are not Cameronians either.

Could they possibly be a Yorkshire regiment?  Though I haven't found any other photos to compare with.

It was probably taken at the time of Queen Victoria's death (early 1901) as the officer centre front is bare headed and is wearing a mourning band.  They could have been in either India or Africa.

Please with any suggestions, which will be greatly appreciated.  Many thanks, Erin Kleinschmidt.