iOS 7 was announced during the first keynote of the Apple Worldwide Developers Conference (WWDC) on June 10, 2013. It was the "biggest change to iOS since the introduction of the iPhone", because the most noticeable change was a change to the entire operating system. In a video that was shown during the keynote, the update had many changes to the app icons, adding layers, and using translucent effects throughout the operating system. iOS 7's design departs from elements like green felt in Game Center, wood in Newsstand, and leather in Calendar, in favor of a flat, colorful design.