If purchasing the ingredients does not cause you to be suspected of terrorism, there's always RetroBrite. Otherwise, be kind to your fellow man, and store up treasure for yourself where oxidation does not diminish it.
That plastics yellow is simply part of the fact that all things in this world are impermanent. Find contentment by refusing to struggle against the inevitable.
This does not, however, mean not being unreasonable at all, since, of course, there is no progress without some unreasonableness.