I now whites can yellow, especially when in direct sunlight, but this is just weird. Here's the problem. I built a Lancia rally car in last december. It was painted white, for which I used Maston's spray paint. (I don't think those are available outsite scandinavia) I applied decals over the gloss white, then sealed them with future. The white paint started yellowing when I was still building. Could this be because of the future applied over the white? When building, I forgot to paint and apply a small hatch on the roof. I then quickly painted (without primer, for the rest of the car I used vallejos primer) and installed it. Strangely, except for the rear of the car, this is the only place where there's no yellowing. And this yellowing can't be from direct sunlight. I built the model with curtains on and stored the finished model in a closed. And I think I had sufficient drying times for the spray paint. About a week. And strangely, my Focke wulf didn't yellow at all, yet I didn't do anything differently.
Now I'm building a Narcissus shutttle for the miniature magic campaign, and that will be white. What can I do to prevent this one from yellowing?

Have you used future as normal on all? Ive read that future yellows with time.. so it may be the cause or even a factor contributing to the cause.
Cant answer your specific question, but it might be worth questioning the use of future. Has it been used every time?

I too think it maybe the future yellowing. I hadn't used it before on white, so the possible yellowing is just about invisible. The small hatch hasn't yellowed and it was painted with just spray white. I think I'll experiment a little before spraying my narcissus.