The overall sentiment for a comment could be different from the topic-level sentiment. A comment could have two tags - say, "professional" and "mistakes." The overall sentiment for the comment could be neutral, but the topic-level sentiment for "professional" could be positive (making that word green) and the topic-level sentiment for "mistakes" could be negative (making that word red).
To see the topic-level sentiment within a comment, you should be in the edit mode (where, as you said, you review the comments when topics are assigned). Click the pencil icon in the top right of any given comment.
Then in the "Edit Records" pop-up that appears, switch from "Overall sentiment" to "Topic Sentiment"
There should be a little drop-down arrow next to each tagged topic that lets you see the sentiment for that particular topic in that particular comment.