Actually, I've remembered I often see this rainbow effect when watching 2GB+ BD Rips as well, which always seems strange and bothers me. With both TV and Movies, I think it tends to be on darkish backgrounds mostly.
Rips are usually encoded with poor quality. Same goes to many tv broadcasts (you need to remember that they are encoded in real time and same mux has mutliple channels that are sharing the limited bitrate so if there is complex frames on all channels at the same time you are more than likely to see macro blocking and other visual encoding glitches).
general: if you suspect there is a codec issue then record a sample and play it on a different device. Over 95% of the cases the issue is in the stream itself.