I had some of my favorite cels professionally 
framed with UV protectant glass some years ago, 
and the colors haven't faded.  ((And I'm very 
paranoid about that sort of thing!))  So I'd ask 
your local framer about that.

If you can't afford the special glass, at least 
be sure not to hang your cels in/or near direct 
sunlight.

Also be sure to protect sketches, and not just 
from sun--- but from cigarrette smoke, warm 
temperatures, etc.

Caroline