The Solid color Saffron kilts (a goldish brown color) are the most "traditional" in the fact that they are colored to look like the Irish Liene (the "kilt like thing" that the Irish wore long ago).
Actually, the leine was "a nightshirt like thing", a unisex garment rather like a woman's shift, often with very exaggerated baggy sleeves.
While not historically Irish, the kilt became popularized in the 1880’s by the Gaelic League and Irish patriots like Patrick Pearse, Bernard FitzPatrick, Eamonn Ceannt, Douglas Hyde, and Pierce O’Mahony, until now it’s recognized as a form of national dress. The most common and widely recognized is the solid colored saffron kilt as worn by Bernard FitzPatrick and Pierce O’Mahoney while campaigning for home rule in Parliament in the 1880’s, by Douglas Hyde, the first President of Ireland in 1938, and by the pipers of the Irish Defense Forces and the Royal Irish Regiment today.