The colon. It can join two independent clauses as a semicolon does; it can link an independent and a related dependent clause as a comma or emdash do; or it can be used to introduce a list in which the items are separated by commas or semicolons. It is our house style (following the Chicago Manual, I believe) that complete sentences that follow a colon are to begin with a capped letter. Fragments or lists after the colon should begin with a lowercase letter.
The squid stared at me in surprise: It had evidently never seen a scuba diver shoot ink back at it before.I hear the pause after a colon as longer than the pause after a semicolon because there should be two spaces after the mark as opposed to one (and the greater the space accorded to anything in a story, the greater the weight it has), and because the cap at the start of a new sentence carries its own weight.
The squid opened its luminescent eyes: vast orbs glowing like Chinese lanterns.
Contact lenses for squids are available in the following colors: chartreuse, periwinkle, lilac, rose, and burnt sienna.