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In older versions of Autocad when you created a viewport and locked it, the frame around the viewport would change color so that you knew if it was locked or unlocked.
Is there a setvar or something that needs to be set so that when you lock a viewport it's frame color will change???
Civil 3D 2014
I'm not aware of any setting that changes the color of a viewport when locked but there is a lock icon on lower right of tray that is blue/locked or yellow/unlocked when the viewport frame is selected or while in MS of the VP.
As I'm sitting here trying to remember, I think this locked viewport color change may have been a toolpac command viewport lock/unlock.