> If any brown M&Ms were found backstage, the band could cancel the entire concert at the full expense of the promoter. I really don't think this would stand up in court. Does anyone know of any concerts cancelled due to minor issues with the rider?
It's only to act as a canary, kind of a checksum (and I suspect it's not the only one, only the most obvious/curious).
When the band arrives into the venue, they check for canaries: if they see something wrong, it's a good enough reason to trigger a full inspection for serious issues.