Way back in the late 90s skeletons were made in "bone" coloured plastic (actually a sort of off cream colour) so you may just have old parts.
With parts that small I wouldn't worry anyway - moulding parts (so you can have a full regiment of skeletons with the same shield etc) is a grey area in the law, as long as they are for personal use, so its unlikely GW could enforce copyright even if they wanted to.