If you attempt to use the Abyss Lord's Abyss Stones or Abyss Fountain when you have insufficient Ability Mana, the message incorrectly shows a green crystal (representing Build Mana) instead of a blue one (representing Ability Mana). These abilities use Ability Mana, and should show message that states "NOT ENOUGH
Screenshot: (Note that I have sufficient build mana for all my defenses. I am attempting to use Abyss Stone here.)
This seems fixed as of update 19.2.