Sony's NXT line transparent bar set as notification light via 3rd party app, Xperia U gets all the colors
That transparent strip which lights up and looks so cool on Sony's NXT design line phones like the Xperia S, P and U, doesn't serve much purpose for notifications.
Granted, on the Xperia U it lights up in red, white, yellow, green, purple and blue depending on the music you are listening to or the theme you are wearing, but that's about it.
Illumination Bar Notification, and allows you to set the transparent strip on the Xperia U to light up in all the above colors for new messages, emails, missed calls and so on.
On the Xperia S and P you only get white color, of course, as that's the only LED stuffed in there, but you can set blinking speeds, and still have a cool notification telling you what's waiting for your attention.
source: IBN (PlayStore)