Pigment Storm

• WWizards of the Coast2021-04-16
  Official Ruling
  Excess damage has been dealt to a creature if the damage dealt to it is greater than lethal damage. Usually, this means damage greater than its toughness, although damage already marked on the creature is taken into account.
• WWizards of the Coast2021-04-16
  Official Ruling
  If the target creature is an illegal target by the time Pigment Storm tries to resolve, the spell won't resolve. It won't deal damage to any player.
• WWizards of the Coast2021-04-16
  Official Ruling
  Pigment Storm's replacement effect is a self-replacement effect. It is applied before any other replacement effects that would change the amount of damage dealt to the target creature and its controller.

Rulings via Scryfall