My opinion only: Yes, I think that the sun is what yellows the Devcon. I tried to spray automotive clear over the devcon to see if it would still yellow and it has not so far. I have been wanting to try some of the UV Blast stuff to see if that would keep it from yellowing. It does take a long time to see a bait start to yellow. I have some that are three to for years old that has not yellowed yet.