Having done a bit of research, especially using data gathered from an esteemed member's column.

The kilt is Scottish in origin, probably 500 yrs old. The Irish, and hence the Scoti, who migrated to Scotland in 300-400 AD wore the leine, a long tunic. This was typically saffron colored, possibly due to washing in iron pots.

The kilt cam later, as wool become more available and its water shedding properties appreciated.