Q. I recently wrote a book where some headings listed tasks and challenges. For example, “Task 1, Learn as Much as You Can about the Disease” and “Challenge 1, Adopt a New Attitude.” Someone told me the punctuation was wrong and the commas should have been colons. I think that either commas or colons are correct. Am I right?

A. You are right—either mark is correct, but a colon isn’t the only alternative to a comma:

Task 1: Learn as Much as You Can . . .
Task 1. Learn as Much as You Can . . .
Task 1—Learn as Much as You Can . . .
Task 1, Learn as Much as You Can . . .

Those examples are listed in descending order of effectiveness. A comma would be most appropriate as sentence punctuation (and we’re styling task numbers like page numbers here; see CMOS 9.26):

Now let’s turn to task 1, “Learn as Much as You Can . . .”

In a heading or a list, either a colon, a period, or a dash—each of which creates a stronger break than a comma—would work a little better at making it clear that “Task 1” is an enumerator and not part of the enumerated item. So you’re not wrong, but your challenger isn’t entirely wrong either.