analog tv tuner signal project

Hi everyone, I need some help with a major project that I am working on. I am working on an analog TV tuner and it has a LA7770 chip inside. I am trying to source the signal that causes the inversion on the TV, the negative film effect. You know when the TV image looks clear, but the color is really funky like looking at a negative picture in the light ? no color ? just an inversion. I hope this makes sense?..? Is there a filter I can build to interface with the LA7770 chip to capture this signal that causes the inversion. I would like to source the signal without any other noise only the filtered signal that causes the inversion. I have looked on the forum for related links with no joy. If anyone can provide some links, book titles, or a filter circuit that can help me out this jam, I would greatly appreciate it. Thanks?.