There have been some talk about applying colors to staves and notes, rests etc. for final output in the past, but this request is a bit different - and, probably… “simpler” 
, considering much of the functionality seems to already be there… (Yeah, I’m a programmer myself - I know “simple” or even “simpler” is never actually likely to be the case 
).
I find that while the comment feature is great, it’s not ideal for getting a quick overview/reminder of different “kinds” of comments - e.g. “TODO”-items while working on a score. What I’d love to see is a way to apply unobtrusive coloring to areas of the score, which could be used for whatever the user wanted - e.g. “check with the musician if this bit is feasible” or for a transcription: “Not sure if this is actually what’s played here, check again later” or “I know the oboe is playing something here, but I can’t hear anything at all… Try again after resting ears”. 
Dorico already has internal highlighting of “event regions” and whole measures on a single staff (as well as support for user editing of their extent) - for highlighting cues, MIDI trigger regions, slash regions etc.
I feel like this could be ideally expanded for more visual “commenting” - i.e. a popover allowing choice of color from some user presets picked from a color picker - or fixed color presets (if the Dorico team wishes to “reserve” certain colors for future regions). Which would then be applied to the selected region, possibly with a “Highlight user markup” menu item in the View menu, much like the items for Dorico’s own highlight regions. Maybe also the option of entering a (short) comment which would be displayed in the same place as the C0 in the MIDI trigger region shown above.
To emphasize: This wouldn’t be for adding colors in a finished score. For that, this would probably not be flexible enough for anyone. Rather, a more visually rich approach to comments. I’ve been “dreaming” of this one since I first noticed highlighted regions back in (I think?) Dorico 3.
Until now, I’ve mostly resorted to adding thick red lines across such a “region of interest”, which isn’t really very aesthetically pleasing - and not very efficient workflow-wise.
Any thoughts?