hmmmmm.....I reckon they used the pigment more in the earlier Amiga's cause the 1200s don't yellow very much, well none of mine have, but all my 500's are slightly off colour, not yellow though. And especially one of my 600s is as ripe as a bannana!
If you look at a pack of cards the 'Spades' as they call they are actually peices of Brocoli you'know!