I was just conducting a search & found this on the Great War Forum regarding khaki kilts:

The Khaki Kilt, aka "Kilt Serge Drab Mixture", was introduced in 1914 with pattern number 8159/1914, pattern sealing date unrecorded however it would be mid Dec 1914. The first contract (C/1481) was issued on 21/1/1915. An improved pattern 8391/1914 was introduced on 28/5/1915 and the existing contract modified. The Priced Vocabulary published in July 1915 lists this item as being in inventory at the cost of 16s6d.

Yes, the purpose of this kilt was to clothe highland units authorized the Kilt on an emergency basis. However, its primary function was to clothe Canadian units arriving in England with Kilts. As all Kilts supplied to Canadian units came from Scottish manufacturers, even before the war, the Kilt manufacturers could not keep up with demand so this was established as an expedience. Tartan Kilts had priority to British (Scottish units). Few, non Canadian Highland units received these kilts. I know of no units being deployed so equipped, however my research is far from complete in this area.

I hope it helps.