Hi MayFlower. Some further thoughts. Multiple colours (as many tartans have) will make printing expensive. Could you look at using various shades of purple with perhaps white stripes in a tartan design. Your 'circle of excellence' could be in gold around a tartan sybol (now I don't know if I'm making sense).
As to Scottish symbols, animals (e.g stag), birds (golden eagle, osprey), heather, claymore (a large sword). also on the main page I have put a website link -
http://www.vanishingtattoo.com/tattoos_designs_symbols_scottish.htm - which may give more ideas. Thanks for your efforts - I like your style.