We use Format > Characters > Red to mark text that is conditional (users here don't like the Conditional Text feature). When books are being finalized, we eiter delete red text or change it back to black, depending on whether it belongs in the book.
It's a minor issue, but Format > Characters > Default Paragraph Font does not always remove the red. I frequently have to change the paragraph style and then change it back to get the normal black text.
I'd like to get a better understanding of what's happening "under the hood" so I can change the text color more smoothly.
This happens when the complete paragraph is assigned the red color. As soon as the complete paragraph has a character format (or a manual override), it becomes an irregular format (shown with an asterisk*) and cannot be reset by "default paragraph format", because the overridden format has exactly this override as the default.
Solution: leave at least one character (e.g. the period at the end of a sentence or a space after the period) without that color/character format, and it can be reset by the "default paragraph format".
re: (users here don't like the Conditional Text feature)
As the internet meme goes, "I think I found your problem."
Why don't they like it? I ask because it's possible that you're not using it optimally. FM has the feature for ease of stewardship for provisional and alternative content. Being Frame, there are usually multiple ways to do a similar thing, but unless you have a very narrow needs, they usually won't be easier.
Character Formats in particular need to be avoided except when they are the only solution. Getting rid of them is often beyond nuisance. I'm right now trying to eliminate some missing-font issues in an older template. The font names didn't even show up in the MIF. They were finally found accidentally in an applied but unobvious Character Format. I'm wondering if the definition was hiding in that hex block starting at <DocFileInfo in the MIF.