Q. CMOS 6.65: “A colon may also be used to introduce a quotation or a direct but unquoted question, especially where the introduction constitutes a grammatically complete sentence.” MUST a colon be used or is a period after the introductory sentence also correct?
A. If it will be obvious to readers how the quotation fits with the surrounding text, a period can work just fine. If not, use a colon.
Jerzy was always talking about how she’s an astronaut. “I’ve been to the moon twice. I have the receipts.” We almost felt sorry for her.
Unprompted, Jerzy announced the reason for her recent absence: “I was on the moon. Again.” We didn’t know whether to be jealous or mad.
The colon is often the better choice; readers tend to appreciate such signals. But a period can be less insistent. Either one is correct.