I had the same problem. I deducted that if my TV worked fine for an hour or so and then the colors became bad (green, people's faces purple...), it must be a overheating problem. Simple logic, right? So, I picked up a few tools and a small vaccum and went to work.
I went first for the main source of heat: The lamp. Just a few screws, and I removed it. The lamp cage has a fine screen to prevent the dust to cover the lamp. Mine was covered with dust! And the fan behind the lamp was also covered with dust! Bingo!!! That's my problem! I cleaned everything and vaccumed all the air vents on the the back of the TV. I put the lamp back and checked that the fan was working. The TV works like new since!
Before you are out of a TV for days and spend an arm and a leg for a "Technician" to fix it (replacing expensive parts that didn't need to be replaced in the first place), try what I described above first. It's very simple and it takes only 15 minutes.
Since my TV is 2 1/2 years old, I purchased a replacement lamp. I know that one of these days it will burn out. I'll be ready and my TV will be working again in 15 minutes!
Since my problem was solved, I didn't go to the next step. There must be one or two other cooling fans inside the TV, but they must be working...