I'm getting ready to sell the wool yarn I got in my Christmas bonanza, but I noticed that some yellowing had occured on some portions of a few skeins of white yarn that had been jammed into a clear plastic bag. This yarn is still in its original wrappers, in beautiful shape and clean, so there's no way anything got spilled on it. Does white wool yellow over time if exposed to light or sun? Can it be bleached or dyed? I'd like to be able to pass this info on to the person who buys this auction, but I know nothing about wool. Please help.