I have one too. I bought it here from NorCalPiper, who bought it from SWK, but it didn't fit him.

Saffron kilts are worn by all the pipers in all the UK Irish regiments and in both the Irish Army and the Irish Air Corps, as well as in Irish regiments in several commonwealth countries.

Apparenty, according to the UK Ministry of Defence the saffron kilt represents ancient Irish dress. By represents I don't think they mean it is identical, just similar. The ancient Irish wore the leine (a linen tunic), which was often dyed with saffron, and there are old drawings and carvings that show a pleated version of the leine, so the saffron kilt represents the lower half of the pleated saffron leine, albeit saffron dye doesn't produce the same colour in a woolen kilt as it does in a linen leine.

Saffron kilts were apparently first worn by the pipers of the Enniskillen Fusiliers, a distinguished regiment raised in Enniskillen, Ireland, which was part of the UK at the time, but is now part of the Republic of Ireland. One person here gave the date as 1859, so that's 150 years ago, and I have seen a photo elsewhere dated 1870 of the Enniskillen Fusiliers wearing the saffron kilt, so the slightly earlier date doesn't seem a stretch atall.

The saffron kilt also fits in with the move to adopt solid colour kilts as Irish national dress in the 1800s, although all the evidence I've seen is that only two colours were actually worn, saffron and green, the latter for more obvious reasons and never by the British Army (LOL!), and if anyone can push the date back further than 150 years I'd be very interested to hear it.