This is a foolproof solution that is kind of like a high school science project.
From your salutation I think you're headed for winter, so hold that thought, but...
Sunlight always cures this problem. Take the decal sheet and tape it up in a southern (no, stupid me, northern window) facing the sun. Leave it there for at least a couple of weeks.
The only danger is if the heat is on and the window gets steamy and absorbs the decal, creating your own stained glass window, otherwise in a couple of weeks, no brown.
This won't harm the decals, but they may be crappy anyways, so I always take a piece I don't need and test it first in water, at which point it's an even bet they'll shatter.
Oh, scan them before you do the step two water test. You then may have an opportunity to print them from a jpeg on a hi resolution printer.
If they shatter, then you can attempt to save them by overcoating the sheet with either Future or Micro Scale Decal Film. Just remember that after this operation you'll need to cut out each decal carefully around the art because it's now got a continuous top coat.
Edit: Gee Jeff, two 1/2 wits like us could be a whole brain!