Any shot in the kitchen or even past the kitchen that is below the knees is a red zone shot— a shot that should be neutralized by giving another below the knee shot back to your opponent.
A shot that is around waist height or “comfortably lower” can be counter attacked. This counter attack is a yellow zone shot that can be struck with some dipping topspin or flat. It challenges your opponent. If they are set for their shot early they can counter attack. If they are pressed they may reset with a dink shot to get back into the power point.
A shot above the waist, that is in your “wheelhouse”, is a green zone put-away opportunity. Typically these shots are dipped hard with topspin or flat at your opponents feet or placed off the court.
Knowing the ball height and opportunity height is critical for good shot selection in pickleball.