UI's like that are not applications; they are actually built into the core of Android. Changing system themes, even on a rooted phone, requires downloading an

UI's like that are not applications; they are actually built into the core of Android. Changing system themes, even on a rooted phone, requires downloading an image specific to the ROM you're running, and flashing that over top of your current ROM. Changing to another theme, or reverting to the standard theme, requires re-flashing your phone every time. That said, I would love to see installable themes where the user can download/select/apply multiple themes on the fly without flashing/rebooting their phone, but at the moment, I think it's a result of Android taking the simple/efficient route for implementation.