It's not normal and is probably due to some peculiarity of your general computer setup and FCS creating some form of conflict.
All I can suggest is try the usual troubleshooting/spring cleaning steps such as Repair Disk Permissions with Disk Utility and trash preferences with http://www.digitalrebellion.com/prefman/
If these measures don't work you could create a new user account and run FCS from that.
I assume that apart from being disconcerting the flashing has no bad effect on the final video?
Studio's right. There might be NOTHING wrong....because you aren't seeing the true image. YOu are seeing Color's interface, that is meant to be used only as reference, as it is far from accurate. Only a signal being fed to an HDTV via an IO card like those from AJA, BMD or Matrox can be trusted. Thus might just be a small glitch in that interface.
Color recommends two full-res monitors as well as a full-re grading monitor. that implies serious video board support; your footer info says you're using "MacBook Pro, OS X Mountain Lion (10.8.3), 15" i7".
Last time I saw that type of artifact, it was from not enough video board causing slow updates.
...just my take.