The notification bar never worked properly on my SP. It would never light up for texts. You can get around this by installing the "illumination bar notifcation" app from the play store. Select Xperia U in the settings to make sure all the different colors work. We shouldn't have to use a 3rd party app for this but until Sony fix this with a firmware upgrade it will have to do. If you're using stamina mode you'll have to add this app as an exception and it will work perfectly.
