Q. My grammar books say to cap the first word of what comes after a colon if what comes after the colon is a complete sentence. I notice you don’t do that in the 17th edition of your manual.
A. Although Chicago style in the 17th edition is to lowercase after a colon unless two or more complete sentences follow, the 18th edition recommends an initial cap for any complete sentence following a colon; see CMOS 18, 6.67.