I've never seen the last couple of flashes, but I'm very familiar up to that point. My mid-2009 MBP has been doing the same thing for years. Apple and an authorized service provider haven't been able to offer any answers. It happens often enough that almost every time I hard restart it, I fry my SATA cable. It's actually currently shut down in that state, and I'm waiting for the refresh.
If you have AppleCare, take it in! If you can get the issue to replicate in the store they might be able to figure it out. Unfortunately for me the only thing they've done is replace my SATA cable and HDD a few times. Good luck!