If I wear the hose pulled up, I almost always wear flashes. And I basically agree with Matt here. While I have and do occasionally wear some tartan flashes (always matched to the tartan), I prefer solid color flashes in a coordinating color.

Moose, flashes by themselves won't make you look too dressed up. If anyone notices anything it will be the kilt. The kilt, worn with hose, solid color flashes, a plain leather sporran, and maybe a knit golf shirt will give you a nice casual kilted look.