Rainbow Piece

The Rainbow Piece is a crafting material used solely to craft the Pot o' Gold, a pet-summoning item. Rainbow Pieces fall from the sky, much like Fallen Stars, except that they fall during the day, disappear at night, and only fall around the St. Patrick's Day season. They are slightly transparent.

Trivia

 * The Guide references that the rainbow pieces are parts of a greater object, the Prism Danann. However, there is no such item in the game.
 * This may be a reference to the Tuatha Dé Danann, a supernatural race in Gaelic mythology.