Does your control appear to be still functioning properly? I believe that border you are seeing is indicative of when Ignition has written a new value to an OPC tag and goes away when the value has subsequently been read back from that item. The duration for which this is visible will then be dependent on the tag group (poll timing) and possibly the device settings.
I am still pretty green with Ignition too, so someone please correct me if I am wrong in any of these details.