Some of the various movies of that time period show some British soldiers in black or dark coats instead of the usual red or khaki.  Anyone got a picture of black coats?  Were they a different branch of service?

Like in this scene at 57:05
https://youtu.be/kjspSfMMZc8?t=3425

Riflemen (95, 60) wore dark coats.

I think a lot of staff officers also wore that dark blue colour, and so did artillerymen.

Remember that's the first Boer war, by the second Boer war it was pretty much uniformly khaki for everyone.

Zulu war it was 'Quartermasters' and 'Surgeons'.  They are VERY dark blue with black piping and braid.  I had one as a kid back in 1965 I picked up in a Portobello Road shop (Junk and surplus shops area then).  

The dark coated 'riflemen' wore Green in the Napoleantic Wars.  Ordinary Brit Infantry then wore red and had smooth bore muskets.

In that particular movie it is Naval Artillery that is wearing the Blue coats.