Its the resin, it can be band-aided but it will keep coming back. The quality resin they use in most CF parts its up to snuff for extended UV exposure. A good sand/polish is your best bet. But the issue then becomes if you cut down too much. It also makes it easier for "fingers" to form. Basically little bump like thinks that go along with the weave. Throwing a clear over it can help but ive heard for some reason most of the time it ends up "fingering" after a clear. My guess is the flex additives being used???
Really, paint it. A color... Or just get used to the yellow. Hell companies like Seibon come brand new with a yellow tint. Resin will yellow with UV exposure, period. Its a matter of when. Nicer resin and UV protectant coatings can delay the yellow but cant stop it completely. These things are also done when the hood is made, so its not really something you can do. As of now you can just hope the yellow hasn't extended too deep and can still be sanded down. Maybe look into some high grade UV protectants to spray on it after sanding.