Have you ever received complaints about white garments turning gray?
One of two problems usually causes this discoloration.
Most whites are treated with fluorescent whiteners or optical brighteners during manufacturing to achieve a desired shade of white. Brighteners decompose with age, exposure to light, or, in some cases, the heat of cleaning. Washing the item in bleach will also destroy the brighteners. Decomposition causes the white fabric to appear dull and dingy, or have a slightly yellow or green color.