What do the different PS button light signals mean?

I have a PS Vita and I keep it in sleep mode on my desk most of the time.

The PS button light is off most of the time, but I see the PS button turning on often.

I know orange means charging, but once in a while it will flash a few times then turn off again, at first I thought it means I had a notification but turning the screen on shows nothing.

Is there a guide somewhere which explains the different signals?

As seen here, different lights display different power states or notifications.

• Solid blue: Plugged in
• Flashing blue: Standby mode
• Slow blue flash: Unread message or information
• Solid orange: Charging, but powered off
• Flashing orange: Battery is going to call it quits soon

There's also the so called BFLOD (Blue Flashing Light of Death) that indicates a problem with the vita itself. You can resort to the initialization menu you get by pressing the power button for 30 seconds and trying the different options there.