Capitalization in Titles of Works
Q. I hope you can definitively answer this question. Should the word following a colon in a sentence be capitalized or not?
A. When a colon is used within a sentence, the first word following the colon is lowercased unless it is a proper name. When a colon introduces two or more sentences, or when it introduces speech in dialogue or an extract, the first word following it is capitalized.
That’s a little more cut and dried than what we’ve advised in the past, but we’ve found that it’s just not practical to make separate distinctions based on criteria like degree of emphasis or formality of the statement that follows the colon. Besides, a second initial capital in a single sentence—colon or no colon—can be distracting.