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 trust in their auditive senses to perceive the Yoshi's location and then attack. As such, Yoshis have to move quietly past them. They cannot be defeated.