The color of the modern saffron kilt is probably much darker than the historical Irish léine. There's an article here in which the author dyed a linen garment with real saffron. It turned out a pale yellow color. Whether the Irish used actual saffron to dye the léine is debatable, as there are other dyes that can produce much the same color as saffron, at a considerably lower expense.

I realize these links are all from the same source, but Kass McGann seems to me to be as knowledgeable on the subject of historical Irish dress as Matt Newsome is on the subject of the history of the kilt. And she emphatically rejects the notion that the kilt was a traditional form of Irish dress. She also gives what I think is a very convincing argument against the existence of clan tartans before the Proscription.