YellowShred
The YellowShred (JP: 黄色い布きれ) is a piece of evidence that can be used in Yellow's Justice ACT.
The YellowShred can be found in the bottom left corner of the Bad Way that Punishes You. The item is next to a campfire, seemingly the reason for the tattered edge mentioned in the flavor text. Alternatively, the item can be obtained from Blue's act.
In the second case of the trial-based battle, it is revealed that Green vandalized Yellow's shirt. The fabric which was left behind was part of Yellow's outfit, as described by the flavor text.