Flashes are a choice. I like the opportunity to color coordinate. Yesterday I wore a freedom tartan kilt (green and blue white stripes) with a black shirt, a white satin tie, charcoal hose, and a navy blue jacket. A pair of white ribbon flashes really helped to bring the look together. But when I'm just knocking around the house, I sometimes just leave the flashes off the garters and have nothing hanging from under the cuffs of the hose.
Score card:
Kilts: 5
Hose: 2 plain, one diced, 1 tartan mogans (footless hose)
Flashes: 2 tartan to match, 3 solid, 1 red garter ties for the diced hose
Sporrans: 1 evening sporran and 1 leather medieval pouch used as a sporran