TWD,
The short answer is: RED. Also, I think the yellow in the illustration you refer to above represents GOLD.
The 14th Bengal Lancers
(officially known at times before the Second Afghan War and again afterwards by various titles incorporating different versions of the term "Murray's Jats") are described in some writings and can be seen in period artwork wearing blue kurtas (Indian cavalry blouses) and solid red turbans with no kullah, as the regiment largely consisted of Jats, which can be described (albeit imperfectly) as a denomination of the Sikh religion. So I suggest using Sikh figures rather than Muslim cavalry troopers with kullahs. There is a c.1900 description of their lance pennons being red over white, but without evidence to the contrary it's probably a good bet to paint them that way for the 1878-1880 Afghan war. I have seen the cummerbund described as "scarlet fringed gold." In general the regiment seems to have had a lot of gold trimmings, for Indian officers on their turbans and also on their sleeves. This is a pretty well-known illustration by AC Lovatt of a Risaldar-Major of the regt. from 1909:

PS. Personally I like the idea of having some blue uniformed Indian cavalry, but if for any reason you'd rather have them wearing khaki, it's not out of the question to paint these guys that way. I don't think I've ever seen a photo or illustration of 14th Bengal Lancers during the Second Afghan War, be it in blue or khaki, so... who knows.