Apple TV suddenly gone to black and white only

I have an Apple TV 4k (black with black remote). It has worked beautifully since I purchased it. This morning, it has gone to black and white (plus grey) only. I have done all the suggestions below, including a total reset. It is still black and white only. It is plugged in to a Sony Bravia 4k smart tv.

When I did the full reset, it appears to have downloaded some software update(s).

An example of why it is definitely the Apple TV that's the issue is that Netflix through the TV remote has colour, while Netflix through the Apple TV remote (or my iPhone) is all black and white.

The TV itself is fine : full colour. Just when I go to Apple TV.

Any other suggestions please? I see the last post that was about this was 2 years ago, and the issue first arose at least 12 years ago. I am truly hoping there is a genuine fix for this rather than simply waiting for it to magically fix itself?