I recently finished Academy's HTL-4 helicopter. Before applying the decals, I coated the areas with Future. The next day, I applied the decals. Everything looked great. The next day, I applied Tamiya Dullcoat. Right away I noticed silvering on the USCG decals on the flotation pods. I hoped that it would clear up when the coat dried. Well, on one pod it did clear up and looks fine. However on the other pod, on about half of the decal the silvering is still there.

First, is there anything I can do to fix it now, short of removing the decal and starting over? Second, what did I do wrong? I've used this same method on most of my models and have never had this happen.

Considering you normally use this method, its quite possible that the decal may have been faulty. I have seen some useless decals in my time, but usually the whole set is lousy. Was the silver decal steeped longer in water to remove it from the carrier ... maybe removing some glue at the same time?
I use future under my decals as well. I also use the micro sol/set system as needed. But before I spray any flat cotes, I always paint some future over the set decal on the day after, with flat coat coming 2 days after! At least this way, if a decal silvers, I can take steps to get it sit properly before flat coting.

Hey Cary, theres certainly nothing wrong in your technique and as Frank had already alluded to, it was most likely some faulty decals.

Me personally though, i dont usually wait an entire day before applying the next clear coat. I usually leave the decal to settle for about 30mins before applying a thick coat of clear gloss. Leave that to dry overnight. I apply a thick coat so that it gets under every inch of of the decal, which forces the decal to go in and round all raised grooves when it dries up. Only then do i apply a matt clear coat.