Well, lovat blue and lovat green would work just fine, and these are color that are pretty easy to fine. You could also wear them with this same tartan in the modern colors, especially with a tweed jacket.

If you wanted to branch out from that, I think a nice yellow or mustard color hose would look great, and would accentuate the yellow stripe in the tartan -- again, either ancient or modern versions.

Then there are those neutral colors that tend to go well with anything. Grey hose, or a tan/oatmeal color. The House of Cheviot has a tan color they call bison that would work well for a casual look.