From the Super Mario Wiki
Blindfold Boos are a rare type of Boo found in Yoshi's Story. As their name suggests, these Boos are blindfolded with a light blue bandana and appear with a pair of big pink ears on each side of their heads. They only appear in Level 6-3, Ghost Castle. As they cannot see where Yoshi is located, they attack once they hear the Yoshies. As such, the Yoshies have to move quietly past them. They are invulnerable.