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Can a device have a different user interface and still becompatible?

The Android Compatibility Program focuses on whether a device can run third-party applications. The user interface components shipped with a device (such as home screen, dialer, color scheme, and so on) does not
  generally have much effect on third-party apps. As such, device builders are free to customize the user interface as much as they like. The Compatibility Definition Document does restrict the degree to which OEMs may alter the system user interface for areas that do impact third-party apps.