Sorry, perhaps I phrased that poorly. I understand that gray is a sign of negative score; I mean to say that it would be helpful to have an understanding of why a comment has been downvoted. Sometimes it's clear; some comments are rude, unhelpful, factually incorrect, etc. But sometimes it's not clear at all: Did people just disagree? Is there a factual error that I can't see? Sometimes grayed-out comments with no replies are really frustrating, because I can't see why they got downvoted. Slashdot's system is nice in that it at least makes people give a hint as to why a comment was downmodded. (I'm not saying I strongly want that system specifically, just something to provide more signal.)