At first glance this looks like the standard full dress uniform of a British regular infantry sergeant serving outside the UK (from the 1870s onwards the white helmet was worn everywhere British forces were stationed other than the British isles).
However, while this is definitely scarlet infantry uniform, the distinctive "Austrian knot" seen on his cuff was not worn by regular infantry, but only by volunteer infantry (in the UK). It was also worn by various colonial volunteer and militia infantry units who were dressed in scarlet. Bearing in mind his white helmet, he is definitely not a volunteer in the UK, so I am certain he is a member of the colonial forces (most of whom were part time volunteers).
He is a sergeant, shown by his rank badge of three stripes and his red sergeants' sash. This sash wasn't worn by volunteer sergeants in the UK nor usually in the equivalent force in India, so we can discount those options; we can also discount Canada as they used a different shape of knot on the cuff; we can discount New Zealand as their volunteer infantry used a dark blue helmet, the same as used in the UK)
This leaves us with the following options where there are examples of units using the the combination of features:
- A West Indian volunteer or militia unit (Not many options, but this basic pattern--including the sergeants' sash--was worn by the Kingston Militia Infantry in Jamaica, for example)
- A Cape Colony volunteer unit (several units wore similar uniforms in the 1880s and 1890s)
- An Australian volunteer unit (similar uniform worn by scores of units in the 1880s, some used the sergeants' sash and some didn't)
His helmet is a smartened shape common for South African units, so my feeling is this is a Cape Colony volunteer. His bugle horn collar badge is the generic symbol of light infantry and rifle corps, but should help narrow down the options.
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