I own a 65" SONY RPTV (KDP65XBR) for almost two years. For the last three weeks or so I started noticing that when the TV is powered on after it has been off for 2 or more hours, the whole picture appears greenish in the begining and it becomes normal after a 60-90 seconds. Can anyone explain why this might be happening?

Yes; it sounds like the start of the 'flickers' which has plagued a lot of Sony owners. If so, it will only get worse. Sony has extended the warranty period concerning this problem. Contact Sony SAYS.