As we all know, Zanz has implemented a yellow spell shard called Shard of Readiness, which had completely broken the creature-permanent-spell trinity and red-green-blue trinity that I had in mind. However, I have already thought of a solution for this:
There can be six shards, represented by the primary and secondary colors of light. There are two creature shards, two permanent shards, and two spell shards.
Creature: red, cyan
Permanent: green, magenta
Spell: blue, yellow
We already have the green, blue and yellow shards, and they follow the above pattern perfectly.
Also, I said that Shards have abilities that affect HP. However, SoR affects creatures. But the pattern can still be salvaged: The primary colored shards will affect HP, while the secondary colored shards will affect other cards. Since the yellow spell shard affects creatures, the cyan creature shard could affect permanents, and the magenta permanent shard could affect spells.