I think you're over-thinking and over-worrying on this.
Two concepts: 1) Utter contrast, or, 2) "tone in".
Go with mustard yellow even if there's no match, or something that might be "reminiscent" of the colours of the kilt. There is absolutely no Highland tradition that I can find of matching colours.
My personal favourites? For formal, my black and white diced hose. For everything else, darkish green, claret, bison, or utter chaos. 
Rev'd Father Bill White: Mostly retired Parish Priest & former Elementary Headmaster. Lover of God, dogs, most people, joy, tradition, humour & clarity. Legion Padre, theologian, teacher, philosopher, linguist, encourager of hearts & souls & a firm believer in dignity, decency, & duty. A proud Canadian Sinclair with solid Welsh and other heritage.
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