On startup apple logo briefly turns red with dark blue background

I purchased a new late 2013 27 inch iMac 3.4Ghz i5. The only thing I did after pulling it out of the box was restore Time Machine from my previous iMac. On startup the machine boots as expected, but gets interrupted by the screen turning a dark blue, and the apple logo turning bright red, for about a second or so, then boots as normal, and opens Mavericks. I've spoken to Applecare - they suggested I re-install Mavericks, which I did. The problem is still there. I've done a hardware diagnostics test - no problems. Though I wonder if it could be a faulty graphics card? As far as I'm aware there are no other issues with the iMac. The machine is under warranty but would love to solve this if possible. Thanks in advance.