I try to match my flashes to a colour in my kilt; for instance, there is a lot of "ancient red" (almost orange) in my Cumming/Buchan hunting ancient kilt, so orange or rust-coloured flashes look good with the tartan.

I really don't think there is a proscribed time to wear tartan flashes; I think it's more up to the individual and his "style" that day.

Cheers !

T.