Another photo of 72nd(Duke Of Albany's Own Highlanders) in Afghanistan c.1879. appears to be the Signals detachment from the assorted paraphernalia on display.
Finally managed to dig out the 1981 Military Modelling Annual, which had an article by Michael Barthorp about the uniforms worn in Afghanistan during the Second Afghan War. following may be of interest;
"As the campaign began in winter,..., the troops wore their homeservice clothing but with the undress serge frock". This possibly explains why some photos of the 72nd such as above show them in scarlet. Though this photo shows the full dress Highland tunic.
He also went on to say that some regiments had also been issued with a sort of Norfolk jackets, described by one officer as being "dull earth coloured". One of the colour sketches accompanying the article shows a private of 8th King's wearing the norfolk jacket over the top of his scarlet serge frock. this is based on photos taken of the 8th whilst serving with the Kurram Field Force(NB 8th were not wearing putteees).
Another of the sketches shows a sepoy of 5th Punjab Infantry in winter clothing, a poshteen over his light khaki uniform,
which has green(similar to Foundry's Napoleonic Dragoon Green) facings on pointed cuffs and collar, kullah and turban fringe.
He makes reference to the fact that many of the British regiments had still not received the new valise equipment(1873 issue) and were still using the old pouch belt equipment. He states 17th, 59th, 63rd, 72nd & 92nd were all still equipped with this old equipment. Battalions thus equipped when carrying their greatcoats or blankets had to wear these "en banderole"