You open the fourth envelope. Inside you find an unusually curt note, which reads:
Reorganize my rabbits. My feisty black demon rabbits must be on the left, and my cuddly white angel rabbits on the right. The rules governing how my rabbits move are trivial - figure them out yourself.

Before you are able to process the strange tone of this note, six rabbits hop over and arrange themselves in a row in front of you: