Don't worry about it. Go to the Yellow Pages and find someone local who can dye it for you. If you buy a navy blue Argyll jacket there is no guarantee it will colour match (and in all likelihood it won't). You'd be far better off spending the money for either a 3- or 5-button vest (get the one you don't have) which will add to the versatility of your Argyll without crowding your closet with a jacket you don't really need.