All these sets have that same look on a non HD gray picture due to the triluminos filters. You mentioned a dark spot, it would be better to call it a dark area.
You will never see this when watching TV so I don't see why you worry about it. Somewhere in these same forums months ago I explained how to get to the service manual color screen displays. Now I forget which post # it was.
If your interested you can enter the sets Service Menu by following these steps. Their is a way to reach some full color screens, white, black, gray, red, green and blue if I remember correctly. You may be able to figure it out once you get the service menu to open. This sequence has to be done at a rapid pace.
Turn off your television. The “Service Mode” menu is accessible only from a direct boot of the TV.
Press the “Display” button on your Bravia remote control, followed by the “5” button and the volume “+” button.
Turn the television on with the “Power” button on the remote. The TV will boot into the “Service Mode” menu.
Last edited by WhiteSands; 02-07-2015 at 08:31 PM.