Ask HN: What do the green usernames signify?

Newly created accounts.

That's not as helpful as you think.

If the answer to a question is in the first page of google results, it should not be asked.

I just happened to google this question and now this post is the first result, so I'd say there was no harm in him asking.

My previous answer (here: http://news.ycombinator.com/item?id=2454874) was: They're greenhorns.