With the Irish National, of course off-white or oatmeal hose would look fine, with green flashes. I would also say bottle green would probably look good, but is this a wool or a poly-blend kilt? A lot of the non-woolen kilts I've seen at the Games and other places have slightly different colors (they look "brighter" to me) and I'm not so sure that hose in colors meant to match the standard woolen tartan shades will always work well with non-woolen tartans. If there is any doubt, I'd take my kilt with me when I shopped for hose so I could match colors in person.
M