Some time ago, there was much discussion on this board regarding whether is was appropriate to wear a matching tartan tie with a kilt. According to a number of pundits, this is something that those who know better just do not do. Ergo, a matching tartan shirt will likely be be considered just as much a kilt fashion transgression. Although I can't claim to be a final authority, I might suggest that a better choice would be to select a solid but complimentary color as you might choose a tie. Traditional kilts, as with other fashion categories, seems to have adapted certain general guidelines some of which may not make sense to the casual observer. Just MHO.