Being able to format certain types of color codes, being able to BOLD, italicize, or underline parts of the text in the Index Cards and Synopsis would make those tools radically more useful.
I would use them to set off certain types of character or emotional beat cues from the story beats, and to draw attention to specific characters, locations, or objects.
Index cards and synopses are plain text areas and cannot accept formatting.
As a workaround, can’t you use the markdown conventions for emphasis?
italics or /italics/
Not perfectly but it still allows you to see what’s important at a glance and it’s surprising how quickly your eye becomes accustomed to interpreting the markup.