Hermione doesn’t wear a dress to the Yule Ball in the books at all. Whaaaat? No, she did not go to the ball naked of course. She wore a robe, not a dress, just like she and everyone else at book-Hogwarts always does. And they are blue, not pink, as the previous answers here mentioned. She was wearing robes made of a floaty, periwinkle-blue material … Hermione’s clothes at the movie version of the Yule Ball is definitely a dress and not a robe. Because of this, I don’t think it fits the short description we get in the book, even if we edit it to the right color. A robe should have longer sleeves than the dress Hermione wears in the movie. The sleeves should go at least to the elbows, but in the movie, it barely covers her shoulders. Movie Hermione has a quite low cut dress, where the short sleeves barely connect to the rest of the dress. But in order to qualify as a robe, the neckline should go at least a little higher, and connect better to the sleeves. This is how Hermione’s dress robes look like in the illustrated version of the Goblet of Fire. I’m not sure if I like the character design of Hermione herself - I imagine her with darker brown hair - but the clothes are very accurate to the book. These robes are clearly based on the book description, and not on making Emma Watson look as hot as possible. They are blue and floaty - and most importantly, it is an actual robe with a high neckline that connects with long sleeves. That is what Hermione’s Yule Ball robes should have looked like if it was based on the books!