Screen Turns Blue?

When I'm watching my 50 inch G HAnz plasma, when the picture from any source ( Decoder / DVD/ Wii) is predominantly white or big coloufull explosions occur, the screen turns blue for 4 to 5 seconds then resets to the original picture. For example if I'm watching a skiing film the entire screen will turn blue then reset then turn blue then reset etc etc. Driving me mad... any ideas please?

All external sources have different inputs ( RGB, AV, )

Mike G
July 2009