I'm sure someone is going to come in with greater knowledge than I have on the subject. But for the sake of expediancy, I'll deliver to you what I believe on the subject.

The Scotti, whom Scotland is named after, were a group from Ireland.

The Irish have many tartans for their counties, and for some Irish surnames. These are from the last hundred or so years.

Irish military pipers wear "Saffron" kilts to this day. These kilts are solid mustardy/orange/brownish in color, and I believe they are from times of old.

Northern Ireland is inhabited by the Ulster Scots. Many of these people, although lowlanders by origin, have tartans and clan associations.

Someone with a broader knowledge of history should explain the Irish/kilt association with a bit of history better than I can ...