Yellow Opera are members of a strange family of artificial Heartless. Almost every Heartless in the family (with the exception of Wizards and Bookmasters) shares a common trait: They look very much like Vivi, and all have names referring to their color and a form of music. An opera is a theatrical work combining drama, music, song and sometimes dance. In this case, the name refers to the score for such a work.
Yellow Opera utilize Thunder magic. They are the fastest of their kind, and dart here and there like bees. Like the rest of their family, Yellow Opera are most common in Wonderland once the Hollow Bastion keyhole is revealed.
An interesting paradox, the plural form for Yellow Opera can be both "Yellow Opera" and "Yellow Operas."
A Yellow Opera has been spotted in a gameplay screeenshot of Kingdom Hearts 358/2 Days.