Apple TV Gen 4 appearing in grayscale only

There is an accessibility setting for grayscale color filter. I wouldn’t know any other way that could result in grayscale (with digital connections). It might be triggered by the Accessibility Shortcut, if part of that setting.

Use Display Accommodations on your Apple TV - Apple Support

The remote might be able to trigger that by accidentally by using the Accessibility Shortcut, in specific circumstances where the grayscale setting is part of the Accessibility Shortcut setting.

Else, have you tried to: –

1. Restart the Apple TV (Settings﹥System﹥Restart).
2. Restart the Apple TV by removing ALL the cables for 30 seconds.
3. Reset the Apple TV (Settings﹥System﹥Reset > )
4. Restore the Apple TV (externally)

Smart kid 😀.

Triple tap Menu invokes the Accessibility Shortcut, as an on-off switch for these ‘favorite’ accessibility settings.

If you have no intention to use accessibility functions through the shortcut, then you can turn off (uncheck) all functions for this shortcut to disable them. That would prevent accidental activation through triple tap. Add (or remove) an accessibility shortcut to Apple TV - Apple Support