You could make tartan ribbon bows such as were worn by the Black Watch and currently worn by The Royal Regiment of Scotland. They're called "rosettes" by the regiment.

Here's a Black Watch kilt with them:



And here's the Drum Major of the Black Watch with his grassgreen bows, and the Pipe Major with his Royal Stewart tartan bows:



and another view of the Pipe Major bows:



Here's Gordon tartan bows I made back in the 1980's and stuck on my Gordon kilt:



Tartan bows on a plain kilt would probably look very nice.