What is the primary limitation regarding the green sky as a prediction tool?

Answer

It is an indicator of severe potential, but not a foolproof indicator that a tornado will form.

While the green color signals a severe thunderstorm capable of producing large hail or rotation, many storms exhibiting this tint never spawn a funnel cloud.

What is the primary limitation regarding the green sky as a prediction tool?
weathercolorskyatmospheretornado