Why do I see green sparkles in my video?

I recently fielded a call from a CE at a TV station. He said, "Why do I see green sparkles in my video?"

I checked in with my engineering colleagues and they had some good info. In the case of a bad connector, part of the signal is not getting through to the input. When the connector is bad and the deserialiser can't detect TRS, the deserializer mutes the output to 0. It can't build black because it doesn't know the relationship between Y, Cr, and Cb so it just outputs 0s. 0 is the default output when no signal is detected. Then you would see green.

Since green and magenta are opposite from each other on the vector scope, if you go past green and wrap around, you get to magenta, and vice-versa. Magenta's value is close to (just short of) 3FF, green's value is close to (just bit bit more than) zero.

0 is a special number limited to TRS and the ancillary pre-amble where TRS is 3FF | 000 | 000 and pre-amble is 000 | 3FF | 3FF. Anytime our gear sees a 0 that is not TRS or pre-amble we turn it into a 4 (an 8-bit 1). The closest legal signal to 0 is 4. A value of 4 would look like green on the monitor.