I stored some folded fabrics under an insulated tin roof, with no light except the small amount that came in over the wall sills where I had 10' porches projecting out. Some the really dark colors (navies, especially),some teals, some reds faded on the on the folds - ALL the folds.6-8 deep.I'm not sure if it was the small amount of light or the heat.

i never had fading problems, but i have noticed that with some plastics there is an odor left in the fabrics. the smell does wash away, but it's an extra step that i'd rather not have to deal with.
as i come to those boxes and/or bins, i have to eliminate them and spend more money replacing them. i can't tell in advance which ones will end up being smelly.

This is me too! Light really scares me when it come to fading my fabrics. I too am fortunate enough to have my fabrics in a closet on shelves and in bins (which also scares me about the plastic). I try really hard not to have closet doors open when blinds are open or when lights are on.

Sun will fade, not just the fabric in your stash, but also the quilts you have on your beds, walls, or display racks. I am careful to make sure that none are in the sunlight. Especially hazardous here in Arizona. Just a thought, but if you hang your quilts outside on a line to dry you might want to hang them with sheets covering both the front and the back to protect the colors in the quilt.

I use a fabric shower curtain in my fabric storage room. It difuses the light, and I can see without raising my electric bill. All fabric is in closed cupboards installed for that purpose.

It is a worry, but quilts that are displayed and exposed to sunlight generally fade evenly meaning that the whole quilt is faded. Not a great outcome, but generally speaking most antique quilts are faded. However, it's a different story for material. Faded fold lines(the parts mainly exposed to light) can and do make the fabric unusable. Or you have to cut away much of the fabric to use it. Folded fabric doesn't fade evenly. Same with folded quilts.

True sunlight will fade fabric. It also will fade furniture and carpeting. Best thing to do with fabric is protect it and use it!!!!!

Some great ideas here and thank you very much