The new icons surfaced on Apple's 'Built-In Apps' page; however, they have since been changed back to the iOS 6 ones.
Notably, GarageBand will now offer in-app purchase content with certain instruments and sounds only being available for a fee. It's presumed that GarageBand wasn't made free earlier due to licensing issues and this is how Apple is working around the problem.
Here's the footnote that Apple posted on the upcoming app:
GarageBand is free on the App Store for all iOS 7 compatible devices; additional GarageBand instruments and sounds are available with an in-app purchase. iPhoto, iMovie, Pages, Numbers, and Keynote are free on the App Store for qualifying iOS 7 compatible devices activated on or after September 1, 2013.
It's now likely that Apple will introduce the new apps during its October 22nd special event to unveil new iPads.
Take a look at the new icons below...