A comment starts with a score of 1. As long as the score is 1 or higher, it stays dark. It starts to fade when the score is below 1. With each step below tha

A comment starts with a score of 1. As long as the score is 1 or higher, it stays dark. It starts to fade when the score is below 1. With each step below that, it fades more. So all the grey means is that someone downvoted it, once, before anyone upvoted it. That happens - someone reads it (or misreads it), decides it's wrong or offensive or whatever, and downvotes. That happens rather often, even to completely innocent posts. Usually it self-corrects after a bit, as others decide that there's no reason for the post to be downvoted and therefore upvote it.