When I got interested in Highland dress over 30 years ago I got every book I could find on the subject, travelled to Scotland to see the portraits in the National Portrait Gallery in Edinburgh etc. My "eye" is a result of all of that looking.

To my eye, tartan flashes look "wrong" because they're not in line with Highland dress as we can view it from 18th century portraits up through the 19th century etc.

They seem to have been cooked up rather recently. I suspect that they were invented by kiltmakers trying to find a way to utilise those leftover strips of tartan..."hmmm...a pity to throw those scraps out...but whatever is small and narrow enough to be made out of them? I know! Tartan flashes!"

Flashes have always been made out of material made in long narrow lengths, "ribbon" if you will. The regimental garters always seem to have been made of twill-weave worsted wool, always red.

Oddly, in the large collection of 1860's portraits The Highlanders of Scotland most men have no visible flashes. That surprised me because the regiments all wore visible flashes. In any case the flashes that do show are either plain/self-coloured/solid-colored or striped. The pipers of the Queens Own Highlanders wore striped flashes.

There are many things which should not be tartan: