Ask HN: Why is the top bar black? (June 13th, 2017)
I suspect it is this:
https://news.ycombinator.com/item?id=14548030
In Memoriam: Charles P. “Chuck” Thacker: 1943-2017
Usually it means someone of significance to the community has died...
Perhaps related to this story?
Couldn't find anything in the news. Maybe someone related to Y Combinator that HN is paying tribute to?