Assuming you're talking about the "no brown m&ms" clause that Van Halen had as part of their tour contract. If so, you might not know that it may have been a form of quality control. Van Halen had a big and complex stage show. A typical show would use 3 18-wheeler trucks, Van Halen would use 9 of them.

The complex contract ensured that they had a stage that could support all the weight of the Van Halen show. That any overhead girders were sturdy enough to hang the things they needed to hang. That the electrical system in the venue could support all their equipment. That the doors were big enough to allow the equipment to be pushed through, etc.

If the band went backstage and saw there were brown m&ms in the bowl, they'd know that the venue hadn't carefully read the contract, so they'd need to double check everything else.