TV sets are not what they used to be. They used to be all analog. The set displayed what it saw, (heard). No signal was noise.
When sets got several inputs, there was a small amount of smarts added. If an input did not have a signal then it would switch to another input. One of those inputs might be a test pattern. Also...When On Screen Display was added the set could put text and some patterns on top of the video. Now the set could overlay text and patterns over the noise, or switch to a pattern when there was no signal.
With 100% digital sets, the picture is de-compressed with a monster computer. (DSP) It can do whatever it is programmed to do when there is no signal. Black, Blue, flying logo…..whatever the programmers whant it to do.