non-tartan kilts on the field.

[Tobus]

Solids make sense as there are some Irish contestants too?

Not to get too technical here, but we're talking about Highland Games. It is a distinctly Scottish sport - at least in this context. There may be Irish, Poles, Germans, and people from virtually all other backgrounds competing (we often have several African Americans competing as well), but the point here is that this is a traditional Scottish sport, and one is expected to pay homage to the tradition regardless of one's actual ethnicity or bloodlines.

And that's without even delving into the whole contrived-Irish-kilt issue...