Screen Freeze With Light Blue Tint

Hi,

I bought a refurbished 15" MacBook Pro from the Apple Store last August (2011 model, I think, running Mountain Lion OS X 10.8.3) and it's been fine up until the past week. Twice now, when the computer has been asleep and I've woken it up, the screen has frozen and has a slightly bleached out and bluish appearance and, unable to see the cursor when I move my finger on the trackpad, I've had to reboot using the power button. This seems to fix it, but I'm worried that it might indicate an ongoing or more serious problem.

Just to clarify, what I see is not a blank, pale blue screen, but the screen as it looked just before the computer went to sleep (background picture, any windows I had open), with a bleached-out, bluish appearance.

I can rule out accidental damage (it hasn't been dropped or had anything spilled on it, etc) but it has coincided with a problem I had with the MagSafe Power Supply. While I was using the computer last week with the supply plugged in, I looked down to notice the insulating layer next to the metal L-connector had split, exposing the wires, some of which had frayed. I switched off and disconnected the supply immediately, but can't say for sure how long the damaged supply was in use before I noticed the problem with it. Neither can I say for sure that the two issues are related, but this bleached-out blue screen problem first arose that day, although the second time it happened (this morning) I was using the replacement power supply which is intact.

Has anyone else experienced this? Luckily, my computer is still within warranty, so I'll call the helpline or visit a Genius Bar, but any other advice would be very much appreciated.