If your summer whites seem a little yellow after dry cleaning, the most likely cause is a breakdown of fabric finish used to make the garment appear brighter and whiter. Bright white is not really a natural shade of fibers, yarns and fabrics. Many times, manufactures brighten and whiten fabrics by using special florescent whiting agents or optical brighteners. Some of these brightening finishes have a somewhat limited durability to use and storage conditions. These finishes can yellow when exposed to light and atmospheric gasses for long periods of time. The areas of a garment which receive more light exposure may show a more pronounced discoloration. In some cases, an entire garment may turn yellow or off-white. Dry cleaning can sometimes accelerate this process, though the change is not due to any improper action taken by a dry cleaner. Almost all whites fabrics will eventually yellow to some degree from oxidation of the original finish, storage and age.