Knight of Grace

• WOTC Official Reminder Textofficial rules
  Hexproof — This permanent can't be the target of spells or abilities your opponents control.

• WWizards of the Coast2018-04-27
  Official Ruling
  Knight of Grace only gets +1/+0 if any player controls a black permanent, no matter how many black permanents players control.
• WWizards of the Coast2018-04-27
  Official Ruling
  If an effect says that a creature loses hexproof or can be targeted as though it didn't have hexproof, this applies to hexproof from black as well.
• WWizards of the Coast2018-04-27
  Official Ruling
  "Hexproof from [quality]" is a variant of the hexproof ability. "Hexproof from black" means "This permanent can't be the target of black spells your opponents control or abilities of black sources your opponents control."

Rulings via Scryfall