"...
This new case is the perfect solution to make your Amiga 1200 bright and shine again and while being made of ASA Plastic (instead of ABS on the original cases). It will no suffer any yellowing."
I don't know if the original was pure ABS though, but seems to have been mostly made of it, at least judging by the yellowing of some old ones..
Then again, there's probably many other things that also yellow....