“Life is tons of discipline. Your first discipline is your vocabulary; then your grammar and your punctuation.... Then, in your exuberance and bounding energy you say you’re going to add to that. Then you add rhyme and meter. And your delight is in that power.”
— Robert Frost, Life Magazine, Dec. 1, 1961 —

COLON

The sign used to mark a major division in a sentence to indicate that what follows is an elaboration, summation, interpretation, etc., of what precedes; and to separate groups of numbers, as hours from minutes (5:30) or the elements of a ratio or proportion (1:2).

Capitalize the first word after a colon only if it is a proper noun or the start of a complete sentence.
The travel agent promised this: Our vacation tour will be the trip of a lifetime. Going global, she told us, will take on a new meaning.

EMPHASIS: The colon often can be effective in giving emphasis.
He had only one hobby: eating.

DIALOGUE: Use a colon for dialogue.
Bailey: What were you doing on the night of the 19th?
Mason: I refuse to answer that.

Q AND A: The colon is used for question-and-answer interviews.
Q: Did you strike him?
A: Indeed I did.

PUT COLONS OUTSIDE CLOSING QUOTATION MARKS:
Johnson emphasizes three elements of what she calls her “Olympic journey”: family support, personal commitment, and great coaching.

— Owl On-Line Writing Lab —