Apple has quietly added a Knowledge Base article that reads, in its entirety:
“If your MacBook is exhibiting discoloration on the top case after some use, please contact AppleCare for service.”
This seems to be tacitly acknowledging the problem I wrote about a while back, where parts of white MacBooks would turn a nasty yellowish brown after only a moderate amount of use. It’s good to hear that they are taking care of the problem, although its cause is still unclear. It certainly isn’t a problem that affects the majority of MacBooks, however.