Phone Question

I haven't been able to find an answer to this. I have a Sony Experia phone. At times of its own choosing, a blue light flashes every 5 seconds. (only when the phone is turned off) It is the same light that is red when it is charging and it turns green when it is fully charged. It flashes whether or not it needs charging and whether or not I have any missed calls or messages. What, if anything, does it mean?

Usually, a flashing LED light would indicate that you have a message or missed call or email or some type of notification on your phone that you have not dismissed yet.

That's what I thought it was, but it does it at any time. I'll just put a piece of tape over the light. Solved.

Edit/Update:
OK. It was a message from a.t.&t. telling me that my plan renewed. (uh, evidently or I wouldn't have gotten the message)
I thought clicking on the notification was enough to cancel it, but I went back to the message and clicked "Got it" and the light stopped. But there have been other times when it started flashing when I didn't have any messages or calls and it stopped on its own.

Sometimes there might be times where you think you don't have a notification but you do. It could be a text message, an email, phone relating notifications, game notifications, anything relating to something on your phone. To make the light stop flashing, you can clear all visible notifications that has popped up. I used to have a phone that the LED light and it would flash red when battery was low, and have a the light turn green, and stay green, if it is charged and until I unplugged my phone. Anytime that my light flashed blue, or any other color, was because of social apps, games, or whatever that game me a notification. And it would stop flashing if I took care of all the notifications.

Thank you. I think some of the times before when it stopped it was because I cleared those automated messages. At least it doesn't beep when it flashes.