One Space or Two?

Q. Help. How many spaces do you leave after a colon in a manuscript?

A. One space after a colon. There is a traditional American typing practice, favored by some, of leaving two spaces after colons and periods. This practice is discouraged by the University of Chicago Press, especially for formally published works and the manuscripts from which they are published.

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]