Create a note using Sorter. If the title contains the “:” character AND the note is saved in Global Inbox the “:”-character is converted to a dash “-”.
If the note is save to any other place the “:”-character is retained.
(The colon is not accepted by macOS in file names. If you create a document in DEVONthink with a colon in the name, then reveal that document in Finder, or drag that document to Finder, the colon will be replaced by a hyphen. In other words, DEVONthink allows characters in document names that the file system does not allow, but behind the scenes the files are stored without the disallowed characters by using hyphen substitutes. Nevertheless, what you reported is a glitch for now.)