Many will say, and I am among them, that it is important to match the fly plaid to the mill run of the kilt. This is true because the fly plaid lays right over the kilt and the differences of dye patterns and weave will jump out.

But with ties, there is always a seperations of colors and distance.

So - when you buy a tie, tartan or solid, just get something that is pleasing to the eye.

This site seems to be a very economical source.