They could accomplish this by using some color that is readable, such as red or purple. That would give a huge visual indicator so that you'd know you are dealing with a dead comment.
Remember, people who do not want to read any dead comments will have left "showdead" in its default state of "off", and so won't see these at all. The only people who see dead comments are those who explicitly said they want to see them.
Is that definitely the way it works? I don't think I've ever configured anything on HN and I see dead comments. I also think it's really nice - as grandparent said, it's a very clear indicator that I'm dealing with something I probably want to ignore.
Ohh, are 'dead' comments different from ones that have just been downvoted into mostly-grayness? In that case I don't actually see them, I just see undead comments :) thanks for clarifying
Remember, people who do not want to read any dead comments will have left "showdead" in its default state of "off", and so won't see these at all. The only people who see dead comments are those who explicitly said they want to see them.