The same thing happened to a piece of my fabric that was pink. It turned yellow and I pre soaked it in Spray-n-wash and it did not come out. I will just cut around it. Mine was stored on wooden shelves and no other piece is like that. Not even my white fabric. I am thinking it is some sort of chemical reaction to fabric. Barnbum was your fabric washed before it was put on your shelf? Mine was not pre-washed. :-(