Question

When using a colon to introduce a list, what must the colon follow?                 

Answer 1

What comes is an independent clause relevant to the list

Answer 2

A colon is indeed expected to introduce a list but the text preceding it must constitute an independent clause making up a sentence that can stand alone.Use a colon after an independent clause that introduces and states the nature of the list that [ follows. The preceding sentence must include a phrase that serves as a generalizing term common to the list elements ]