While browsing through an ACT study guide, I have encountered the following sentence (as part of a discussion of old signs seen along the highways):
After all, there they are: advertising products and businesses that no longer exist.
The study guide claims this sentence is grammatically correct. However, most grammar guides seem to insist that the clauses on either side of the colon should be independent in such cases. The post-colon clause in this example is definitely dependent. How is this okay?