non-tartan kilts on the field.

[TheOfficialBren]

Hummm, on balance I think as people are competing in a Highland Games and at specifically Highland Games type events then I think tartan kilts really ought to be the way to go. If nothing else and at a guess, I suspect the spectators might expect it.

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Traditional tartan (or tweed, I suppose but that might confused the spectators in many ways [to riff off of Tobus' post about those phoney Irish kilts]).