Color coding the comment stickies may be hard since there could be replies from multiple people on the same sticky.
I agree with the need for a quick visual cue though, and for this reason I created custom color-coded icons for each department that I assign whenever I create new profile. I hope this idea might help as an interim solution for anyone else that wants to clearly see which department added each comment and reply.
These can be set on each user's individual profile, though unfortunately you cannot apply icons to multiple profiles at once.
Found out that if someone just has a reviewer license and no proof license, they cannot save a default color for their markups like others can. That makes the need for something like department or functional group coloring more important.
