I have a long standing rant about not italicising colons. It not only affects grammar, but also Note: and Example: introducers. One day we'll get to it.

@tkoeppe: Do I interpret this correctly that you want the colons to be italics in these cases?

@jensmaurer: No, heaven forbid! The point is that punctuation should never be italicizable. Italics are letters, but it really doesn't make sense to incline commas, periods, colons, or even brackets. Slanted brackets are an unfortunate outcome of digital typography (where the layman's idea of "italics" is to just shear the shapes a bit) gone wild. Good fonts keep the punctuators straight even in the italics.

I want to style notes and examples as [\textit{Note}: and --- \textit{end note}]. And we should find a similar way to make the colon after grammar productions appear straight. It's even more obvious why that's the right thing to do in that context: the colon isn't part of the production!

@tkoeppe: Thanks. Does @zygoloid agree with this direction?

Ah, it seems the colon after preprocessing-op-or-punc, while upright, is actually \ttfamily, which is also not what we want.

@jensmaurer: No, we never reached a conclusion on that. It's one of my big plans for C++20.

Fixed by ffb9408. Thanks for providing the solution!