If you have the Sony Xperia U AND have rooted your handset, then you may want to check out the LEDs U CTRL app. Whilst the phone’s transparent bar can illuminate in different colours depending on what content is displaying on screen, this application allows you to individually control the LEDs in the strip.
LEDs U CTRL will allow you to show notifications for 20 different app alerts (missed calls, SMS, calendar, GMAIL etc). It’s fully customizable too, allowing each individual LED to light in 1 of 16 colors. It also allows you to configure the speeds of the LED, the time the LED is at full power, the time between blinks, the number of loops per cycle and CPU speeds during the alerts, amongst other things.
There is a free app to see how things work where you can create and preview your notifications. However, to actually use it on a day-to-day basis you will need to pay for the LUC.radar app that costs £1.56. Remember, this only works on the Xperia U and your phone MUST be rooted. Sounds like a cool little app if you like tinkering with your phone.