I don't have the link any more but there was a nice article and discussion somewhere about the Super Nintendos yellowing and the conclusion was it had to do with how well the plastic was mixed with the flame retardants and what sort of fillers might be used. Exposure to open air/UV/etc. interacted negatively with the mixes that were too far off. If the mix is how it should be and without cheap fillers, you won't get any yellowing, or very mild amounts. And of course every time they make a batch it can come out differently, which is why on some SNESs, half is yellowed, half is perfectly fine; the parts were from different batches.
For lightening Macs I just use an even 50/50 mix of Clorox Outdoor and water, give it some good sun exposure and spray it over 3-4 times. Even very badly yellowed Macs I can at least get down to a much more pleasing beige color. Milder yellowing can turn out virtually indistiguishable from the original platinum. The process preserves the texture but does kill some of the sheen. Still experimenting with the best ways to restore that.
One thing to look out for: some Macs have that silver/grey paint that's used as an EM shield in place of real metal. Don't let it be exposed to any cleaners and not even water if you can help it, otherwise it'll crack and peel into a horrid glittery mess.