Yes I agree with Melanie. Even a standard TV signal is a very specialised thing. Essentially analogue in nature and very fast with a solid time structure! I was associated with electronic image generation in the pre PIC days. Although it was done using relatively simple logic chips, this type of circuitry could often 'think' about several processes at once and extremely fast. A PIC cannot. It is possible to do what you are hoping with a PIC but speed is important as well as the the fact that you are forced into synchronising the program processing in the PIC with the TV signal scanning speeds. Using a certain amout of extra hardware may make things easier for the PIC.
I will send a longer message when I've got a bit more time but I would strongly advise doing a bit of reading up on TV signals. Don't worry too much about how colour information is portrayed for now. The most important part of a TV signal is actually a hign definition black and white with infinite number of levels (being analogue). Sync pulses are included to synchronise the TV to the signal.

John R