Ditto what Greg said. I've read a bunch of comments about it being the white paint that yellows, but for me Testor's Dullcoat and Glosscoat get a tinge over all colors over time. I have been using Future for about a year now. No yellowing at all. You can see this on rockets next to ones with Glosscoat. There's a pretty big difference. Best airbrushed on, but you can also wipe in on with a cloth or even a paper towel. If you use acrylic paint, though, make sure it's good and dry before using Future. It can make an excellent paint stripper, too. Trust me!
Drew Tomko