Isn't spell correct fun?:

When in doubt, use less concentrated hydrogen peroxide. My approach was to use the really weak stuff from Walgreens and mix it with more water, and just put in a scoop of oxi clean and stir, and leave the parts in a bath while out in the sun. It produced more even results for me at the cost of requiring far more exposure time. I did it to a few of the parts of my Apple IIgs with no ill effects.

Follow that guide to the T. If you gimp on the ratios, you will end up with a bowel of white goo. If you do it correctly though, you will be more than satisfied. 

There is also a follow up procedure that ensures the plastic will never return to yellow. I will get you a link shortly...

So hydrogen peroxide and laundry booster mixed should do the job thanks.

http://retr0bright.wikispaces.com/

It's a process known as retr0bright. The link above might help.

I believe if you put some lemon juice on it and lay it out in the sun it should work.

Hey everyone I was just wondering how I would go about removing yellowing from a white gameboy play it loud.