Many people who jumped on the PC bandwagon early probably has electronics that have long faded to yellow ("or worse, brown") lying around. The Retr0bright Project thinks it has found a way to restore retro hardware to their original white color. In fact, the solution they share dates back from 2008.
A chemist working for a German museum found that dipping the faded plastic in a Hydrogen Peroxide solution actually undoes the yellowing process—previously thought to be irreversible. Further refinements illustrated that using a UV lamp actually accelerated the whitening process from days to hours!
You can find complete details here. Support from those who've actually pulled this off are available through this forum. Hydrogen Peroxide, while commonly used to bleach hair and disinfect wounds, remains a dangerous substance in high concentrations. It was after all used as a rocket propellant.