Apple has decorated the exterior of the Yerba Buena Center for the Arts for its Sept. 12 media event, leading to informed speculation that the artwork hints at a stretched iPhone screen. Based on a reader’s tip, a report at MacRumors suggests that the colors on the facade are actually stretched-out iOS icons, in an ode to the next iPhone’s taller 4” display. Stretched versions of the iTunes, Music and Game Center icons, among others,…