Originally Posted by gojiberry

Moulds will not grow in vinegar which is why we pickle them in the first place. Shallots pickled at home will usually get a yellow discolouration but doesn't affect the keeping qualities or the taste. One way of reducing the yellow is to well salt them before pickling this will draw out juices including some of the yellow colouring. It also makes the onions crisper. Just make sur you wipe all the salt off before putting in the vinegar.

Ian