While there's still time before the season finale, American Idol decided to try something different as the competition slowly gets into the live show portion of the season. As for what the surprise is,

The contestants’ voices are the most important part of the show, but at the end of the day, American Idol is about producing a star, so the look is also vital. Once the live rounds begin, the upped production value is evident, and that’s because wardrobe, hair, and makeup come into play in a much bigger way by that point in the show.

Underwood won Season 4 of the singing competition show in 2005, and recently returned for Season 23 as a judge.