Saffron

Though the origins of the Irish kilt continue to be a subject of debate, current evidence suggests that kilts originated in the Scottish Highlands and Isles and were adopted by Irish nationalists at the turn of the 20th century as a symbol of Gaelic identity. 

Solid-coloured kilts, most notably saffron or green, were first adopted for use by Irish nationalists and thereafter by Irish regiments serving in the British Army, but they can often be seen in late 19th and early 20th century photos in Ireland especially at political and musical gatherings, as the kilt was re-adopted.

A garment that has often been mistaken for kilts in early depictions is the Irish 'lein-croich', a long tunic traditionally made from solid-colour cloth, with black, saffron and green being common. Emulating this garment may be the philosophical reason behind saffron ("the colour of kings") being adopted for the first Irish kilts.