I noticed that someone was asking about yellowing here is how I answered a similar question on yahoo answers recently…
Here are some ideas for you:
Yellowing – Always read and follow the care instructins and any warnings on the garment label. And, follow the General Rules for stain removal.
Some fabrics which are white or pastel colored contain optical brighteners or fluorescent whitening agents (FWAs) which were applied during manufacturing. These agents can decompose when exposed to light and atmospheric conditions, or prolonged storage conditions. In some cases the entire fabric becomes dingy or develops a yellow cast. In other cases the yellowing develops only where exposed to light. The FWAs can also be damaged by the use of chlorine bleach.
Unfortunately, once the FWAs are damaged, the whitening agents can’t be reapplied to the fabric.
All fabric bleach or the use of speciality products available in grocery or drug stores, such as Rit’s “Whitener and Brightener” may help. Carefully read and follow the instructions on the product label, and check for colorfastness first.
another tip to look at :
Dinginess, Yellowing, Graying – Always read anbd foolow the care instruction and any warnings on the garment label. And, follow the General Rules for stain removal.
There are several reasons why fabrics gray, yellow, and become dingy, including not using the right amount of detergent (i.e., using too much or too little detergent), insufficient rinsing, and/or the wash water temperature is too low. To reburbish clothing from these discolorations:
Wash with a permanent press cycle in hot water, use a cool-down rinse on permanent press and use one cup of water conditioner instead of detergent.
If the discoloration remains, either repeat this procedure or wash with the correct amount of detergent and either all-fabric bleach or chlorine bleach, if safe for the fabric. (always check for colorfastness first.)
If the fabric is white, consider speciality products available in grocery or drug stores, such as Rit’s “Whitener and Brightener” to whiten the fabric.Always separate and wash your whites separate from colors. And, don’t put heavily soil garments with lightly soiled items.