https://www.tvinsider.com/679724/american-idol-live-shows-theme-disney/

"I think the producers wanted to do this for a long time when the show was on Fox," says Robert Mills, ABC's head of alternative programming, of the advantages of Idol now being on a Disney-owned network.

Katy Perry dressed as Snow White for American Idol's Disney night (http://www.dailymail.co.uk/tvshowbiz/article-5672463/American-Idol-Katy-Perry-stuns-Snow-White-Disney-Night-field-narrows-final-seven.html)
The singer looked like a dead ringer for the iconic Disney princess.