Hopefully washing them will get it out. A hint to keep it from happening is to throw a dryer sheet into the drawer or bin that you keep the stash in. It not only helps with the moisture, but also the musty smell and little bugs. I buy the cheap ones at the dollar store and also throw them in with the sleeping bags, the back of the linen closet and when I store the winter coats. You can also use bay leaves, but they are more expensive. Another tip for storing your orphan blocks (I keep extras and testers for later use on tote bags as quick gifts) is to keep them in a pizza box - obviously not a used one! Usually a pizza shop will give you one or two and the medium size is great for most blocks. The cardboard wicks moisture, they stack flat and you can write on them. I have a stack of 'patriotic', 'christmas', 'earth colors', blues - etc. I like to try out new patterns or color combos before I go for the whole quilt top.