A few years ago I stopped wearing flashes when I am dressed casually. I just use elastic garters with Velcro.

When I put on a tie and jacket;
I color coordinate (but not match) my flashes with my pocket square.
I coordinate my hose with either my shirt or my tie.

I no longer attempt to match my hose or flashes to my kilt. I figure the kilt is very capable of standing on its own.

I have a trick I do for customers. I will show them that my shirt and hose are coordinated. I then walk over to my rack of kilts and start to pull off different Tartan kilts. As long as the rest of my outfit is coordinated I can look good with almost any Tartan.