Has a new feature been added by one of the recent updates to Premiere Pro CS6? Behind the numbers on the timescale bar at the top of the timeline window is a draggable blue shaded area which can be expanded or contracted (the cursor turns to a red square bracket). I've highlighted in the red box in the attached image.
What does this signify? I can't find anything online or in the Classroom In A Book! It doesn't seem to do anything obvious that I can tell and it's driving me nuts trying to work it out! (It's late and I'm kind of over tired). Help, I want to sleep :-)
If you mean the greenish blue shown below it is the result of setting an in or out point (or both).
Just hold the Alt or Option key while clicking on both the in and out buttons. It will go away.
Edit: I see you added the image after I read your post. So yes, it is the result of marking in and out points.
Thanks :-) I must have set them accidentally. I hadn't realised you could add in / out points to sequences as well as clips.