Blue Witch's Sapphire Amulet

Blue Witch's Sapphire Amulet enters the
battlefield tapped.
{t}: Add {u}.
Rainbow: (As long as one mono-color permanent of
each color is in play, the game has rainbow) Sacrifice
Blue Witch's Sapphire Amulet: Search your
library for an Blue Aura or Instant and reveal
that card. Shuffle your library, then the card on
top of it.
"Its super-cold crystal lattice is encoded with such
clever spells."