They were famous for having a clause in the preparation checklist, that they had to have a bowl of M&Ms in the lounge, but no green ones.
Eddie Van Halen was asked about this, and his explanation was that their stage set was very complex, and required rigorous preparation. Failure could actually be dangerous (think the “pod” scene from Spinal Tap).
He said that if they found green M&Ms, then that meant the instructions were not read correctly.
[EDIT] I was wrong. It was brown M&Ms