Awhile ago I placed a very large order on Bricklink to the Czech Republic for a fair quantity of white LEGO bricks/plates, etc. Some of these I ordered in USED condition to save a good deal of money. However, everyone who has an old collection knows, that among their whites (and sometimes blues and greys), lie the dreaded yellowed/discolored pieces.
The plight is certainly common to any longtime LEGO owner, and until relatively recently was a problem unsolved. Enter Retr0bright (follow the link