Substandard video output from Consoles on Bravia TV

I have a Sony Bravia KDL46HX923. Directly connected via separate HDMIs are a Sky+ HD box and a games console (formerly a PS4, now an Xbox One). Some months ago while playing my PS4 the TV display began to flicker intermittently between normal and washed out. To elaborate – there is a permanent 'vignette' or halo on text, graphics and the screen edges. What were solid blocks of colour became patchy. Resolution/fidelity is reduced and the whole screen looks washed out. After a short period of flickering it would settle back to normal. At no time was there loss of picture or sound. This occurred every time I played from then on. Over the months it took longer and longer to settle back to normal. Now it is permanently set on 'washed out' from start up.
 This affliction only applies when I’m in the front end menus and in-game. Playing DVD/Blu Ray is fine.
 Throughout this period, the Sky+ HD box has displayed fine on the TV with no issues.
 Solutions attempted:
 Swapped Sky box and console HDMIs – NO CHANGE
Tried different HDMI lead – NO CHANGE
Tried different HDMI ports (x4) on TV – NO CHANGE
Tested all variations of console Picture settings – changing 'Deep Colour Output' rectified it on two occasions, not since.
Checked TV Firmware – its up to date.
Tested all variations of TV Picture/Display/Screen settings – NO CHANGE
Factory Reset ('Initialised') PS4 – NO CHANGE
Factory Reset TV – NO CHANGE
Convinced it was a faulty PS4 (Id read a great deal about HDMI ports becoming faulty) I admitted defeat and went out and bought Xbox One. The exact same display problems persist with the Xbox!
 I can now reasonably conclude that the TV is the problem, but only when using consoles in the front end menus and in-game. As I said, Sky picture is fine, watching DVD/Blu Rays via either console is fine, watching films from a HDD is fine. Is this a HDMI 'Handshake' issue? If so why does it only affect some of the console video outputs?? 
 
Im spent. I can fine no similar examples of this problem in any forum. I have a fantastic TV and console but am currently left with no option but to play with a substandard display?! First world problems yes but I hope somebody out there can sympathise and offer up any solution short of getting a new TV!!