Why are there no yellow shards?

[MasterfulOverlord]

It seems as though yellow shards were replaced with purple shards, and I'm curious as to why. Any answers are appreciated.

[Rendolf]

As you can see by looking at the top left corner of this page, Reborn's signature colors are blue, red, green, and purple. That theme appears in a ton of places throughout the game. You find out why from the story before your fourth gym battle, if you haven't already gotten there.

[MasterfulOverlord]

Ah, that makes sense. Thanks! Really cool that they added that level of detail.