Very few people, if any at the event, are going to have a clue about Highland Attire, or its casual cousin. The Purple Hose are fine. You do not need to fret all this colour stuff most of the time. The only time it is important is when playing in a band or other situation where it is a uniform. The rest of the time is yours and your son's choices. Where the two of you are playing together, it would be good appearance to dress in your own "uniform".

Slainte