Halo Hunter

• WWizards of the Coast2009-10-01
  Official Ruling
  Intimidate looks at the current colors of a creature that has it. Normally, Halo Hunter can't be blocked except by artifact creatures and/or black creatures. If it's turned white, then it can't be blocked except by artifact creatures and/or white creatures.
• WWizards of the Coast2009-10-01
  Official Ruling
  If an attacking creature has intimidate, what colors it is matters only as the defending player declares blockers. Once it's blocked, changing its colors won't change that.
• WWizards of the Coast2009-10-01
  Official Ruling
  Halo Hunter's triggered ability isn't optional. When it enters, if you're the only player that controls an Angel, you'll have to target an Angel you control.

Rulings via Scryfall