Here is a link and a quote from there in regard to storing on cardboard bolts.
http://www.freepatterns.com/content/content.html?content_id=614
"Hello! I work at a quilt shop and would like to pass on a tip. Please tell your readers to never store their stash on cardboard bolts as they are not made from acid-free cardboard. These boards will discolor your fabric if you let it 'age sufficiently on the bolts,' as my friend stated it. I hope this helps."